He had been incarcerated for more than six months.
El-Erian, 51, had been arrested on 6 May just hours before nationwide anti-government protests that police alleged he helped organise.
He attributed his release partly to Egyptian media pressure in the run-up to the 9 November parliamentary elections and recent protests by the Brotherhood and rights groups.
Since 1995, el-Erian, a former lawmaker, has spent five years in jail on charges of belonging to a banned group that sought to create an Islamic state in Egypt.
The charge and subsequent arrest automatically disqualified him from running for public office again.
But the Muslim Brotherhood is moving ahead with its plans to make gains in the upcoming elections.
The group has announced that it is planning to field 150 candidates in upcoming legislative elections scheduled for 9 November, but el-Erian is not expected to run.
On 8 October, Wafd, Tagammu, Nasserist and eight other opposition groups formed a new coalition - the National Front for Change.
While the Brotherhood will coordinate efforts with the National Front, it will field candidates of its own, independent of the coalition.
Aljazeera.net: What were the reasons behind your arrest this time?
Essam el-Erian: Demonstrating, organising demonstrations and being a member of an outlawed group.
It was rumoured that you had been arrested because you had told your wife on the phone you wanted to run for president. Were you planning to run for the presidency?
I said in previous interviews that the government prevented me from running for parliamentary elections by putting me in jail for five years.
If they ever believed I intended to run for the presidency, they would have executed me. I was kidding with my wife and asked her if she wanted to be Egypt's first lady and we laughed about it.
Nothing was serious.
But let me tell you, this is a very dangerous indicator because this story tells you that this seat or position (presidency) is reserved for one person only and no one is to dare to so much as think about it.
Did the government keep you in jail in the run-up to the presidential elections because it viewed you as a political threat?
That's what it looks like. I was very vociferous in my protests against government policies, especially when it came to the constitutional amendment of Article 76; this was annoying to some people in the regime.
What role will you be playing in the upcoming parliamentary elections since you have already been barred from running as a candidate?
Due to my previous experience in both running for the elections and as member in the parliament, my role in the coming elections is to support our candidates in the campaign and also to support our existing parliamentarians.
How many seats do you think the Muslim Brotherhood can win?
That depends on the fairness of the elections, of course. If it is fair, I think more than 50% of our candidates will win seats. That means around 70 to 80 seats.
How many seats do you think are needed in parliament to form a reasonable opposition to the government?
Some observers say a total of 100 seats should be adequate for all opposition groups. This is a very small number in my opinion. If we win 1/3 (150) of the seats ... that will be very good.
It will mark a great beginning for the new session of parliament and translate into tangible political reform.
(Egypt's parliament is comprised of 444 seats, with an additional 10 filled by presidential appointment.)
Why is the Muslim Brotherhood restricting its role in the National Front to coordination rather than fully-fledged participation?
Primarily, we already formed a political platform and chose candidates four months ago, well before the National Front was formed.
Our candidates will not run under the National Front's banner but will be independents for the parliamentary elections.
Nevertheless, since we are coordinating with this opposition bloc, we are ready to help them in any way possible in the upcoming elections.
Do disputes exist within the Muslim Brotherhood regarding the use of international monitors in the upcoming elections?
Monitoring of the elections is in our opinion something desirable, of course, but we still haven't decided if it will ultimately be better or not for the opposition to call for such a body.
Besides, there is already a form of international monitoring if you consider the media coverage by satellite news broadcasters, newspapers and magazines from around the world.
Why is the Muslim Brotherhood running under the same slogan as years past: "Islam is the only solution"?
Why not? This is our slogan and our idiom and there is no way you can deny a group to adopt the slogan of its choice. It doesn't matter what slogan we choose. If we change this current one to something else, we will still be criticised.
President [Hosni] Mubarak said that he will nullify the emergency law enacted since the late president Anwar [Sadat]'s assassination in 1981. However, he said he will enact the anti-terrorism legislation. Will this affect the efficacy of opposition groups and other political movements?
I am afraid the new anti-terrorism law will be even worse. Our experience with the regime indicates that they do not work for a better future for the people but only for acquiring more power. Consequently, any new law will be twisted to serve their means and needs only.
How do you view the current trend of political demonstration in most Egyptian universities calling on political reform?
I believe this is a very good indicator of grassroots movements. They should keep for demonstrating for more reform and change. They organised themselves in the summer and were ready once the universities open.
Critics of the Muslim Brotherhood have questioned how often you ally with different political parties - once with the ruling National Democratic party (NDP), once with the al-Ghad opposition party led by Ayman Nour and now with the opposition front. Why so many alliances?
This is how the wheel of politics churns. Political survival means coordinating with others and making deals. Why not, it's not contrary to Islam.
Yes, but doesn't this mean that your main concern is the group's interest and not necessarily the nation's?
I think the benefit of the country coincides with the benefit of the Muslim Brotherhood and other political groups.
It's not a contradiction to seek what will ultimately benefit you and serve your interests if in doing so it does not harm or conflict with the interests of the nation itself.