The Brotherhood, Egypt's largest opposition group, said the arrested men had taken part in protests against the country's Gaza border policy and the Israeli blockade earlier this month.
Another 30 members were arrested at the time of the protests during which activists attempted to get a convoy carrying medical supplies into Gaza via the Rafah crossing.
An Egyptian security official, speaking on condition of anonymity, confirmed most of those arrested were involved in the medical supplies convoy protest and could face charges of belonging to a banned group.
Egypt occasionally permits people to enter and leave Gaza via the Rafah crossing, the only border pass not directly controlled by Israel, but has refused to open it permanently.
It is unclear exacly how many Brotherhood members continue to be detained in the past month since the convoy failed to cross into Egypt.
The Muslim Brotherhood is formally banned in Egypt but fielded independent candidates in the 2005 parliamentary elections, winning a fifth of the seats.