This is according to political sources and relatives of prisoners.
"We counted until now the release of at least 80 prisoners who had joined their families late on Tuesday. Among the pardoned detainees are Ali Laarid, former Nahda spokesman, and Ziad Dawlatli, a top Nahda official," one political source said on Wednesday.
Most of those pardoned would have spent between just a few months and less than two years in jail, one source said.
Political sources described the pardon as a humanitarian gesture made in the Muslim month of Ramadan.
"The pardon would bear a political significance if it had included those jailed for 30 years like Sadiq Shourou, the former Nahda chairman, but it did not," said a political source, who like other sources, declined to be identified because of the sensitivity surrounding Islamist detainees.
Tunisian authorities brand the banned Islamist Nahda group as a "terrorist organisation", which they say had been wiped out early in the 1990s. Its leader Rashid al-Gannuchi lives in exile in the UK.
The government, which denies Tunisia has political detainees, has said only that bin Ali had pardoned "some prisoners" before the 17th anniversary of his 7 November takeover.
The move came 10 days after bin Ali's sweeping re-election win to extend his rule by another five-year term.
Some Western diplomats say the 94.4% popular vote bin Ali won in the 24 October election, less than the over 99% registered in the previous polls, might herald more tolerance of dissent, especially since he had promised greater democracy.
Human-rights activists in Tunisia and abroad say the first test for the re-elected president would be whether he grants amnesty to the 500 or so political detainees in the country's jails.