A security official said: "Under the presidential amnesty, 627 people were freed. There are still 36 detainees who are already on trial now. They may be pardoned after their trial."
A group of parliament members held talks with supporters of Hussain al-Huthi, an anti-American al-Zaidi cleric, in recent weeks to encourage them to stop fighting under an amnesty offered by Ali Abdullah Saleh, the president, in September.
The pardon excludes 36 suspects on trial on charges of mounting a series of attacks on security forces in the capital, Sanaa, last year in which one soldier was killed and 27 people were wounded.
They are also accused of plotting to kill the president.
Several hundred soldiers and rebel fighters have been killed in years of clashes in the northern province of Saada.
Yemen accuses al-Huthi and his supporters of wanting to install clerical rule and of preaching violence against the United States and Israel.
Al-Huthi was killed by the army in September 2004 after leading a nearly three-month uprising in Saada in which more than 400 people were killed.
His father, Badr al-Din al-Huthi, is considered the spiritual leader of his Faithful Youth movement and was accused by authorities of leading a second revolt in March-April last year in the mountainous northwest, near the border with Saudi Arabia, in which hundreds more died.
Al-Huthi was killed in clashes
with Yemeni troops
Fifteen fighters and five army soldiers were killed in fresh clashes in Saada last month.
The al-Zaidis are a Shia offshoot and are dominant in northwestern Yemen but form a minority in the mainly Sunni country.
The al-Zaidi fighters reject as illegitimate the republican regime that seized power in a 1962 coup known as the 26 September revolution, overthrowing the al-Zaidi imamate.