More than 100 other al-Muquatila members are believed to be in prison
Libya has freed 90 members of a banned Islamic group from jail after talks negotiated by a human rights group headed by the Libyan leader's son.
The BBC's Rana Jawad says there were scenes of jubilation at the prison and one man kissed the lens of a camera.
She says most of them are known to have been charged with belonging to a political party, which is illegal.
But Muammar Gaddafi's government said the al-Muquatila group members were planning acts of violence.
In 2006, Libya also pardoned more than 80 members of the banned Muslim Brothers.
Our reporter in the capital, Tripoli, says the negotiations are part of Saif al-Islam Gaddafi's national reconciliation plan, which he brands as "Libya's Tomorrow".
Released prisoner Yaseen Bleblu told the BBC he was released on condition that he abandon political activities and "strive for the building and the future of the nation".
"This is a blessed time... one cannot describe the emotions," said another freed prisoner, Fathi Usef Al-Mgarief.
Saif Gaddafi, the second oldest of long-time leader Col Gaddafi's seven sons, has a reputation as a reformer.