The state also pardoned two others abroad, including opposition leader Hassan Mashaima, an MP told the AFP news agency.
The move late on Tuesday comes after state media reported that King Hamad bin Isa al-Khalifa had ordered the release of prisoners, a demand of protesters seeking an elected government in the country.
Ibrahim Mattar of the Shia Wefaq party told the Reuters news agency it was a "positive move" but that dozens still remain in jail.
"Allowing the people to protest and releasing those people are positive moves," he said.
But Mohammed al-Tajir, a human rights lawyer representing some of the detainees, said he was not sure that the release of prisoners would be enough to satisfy protesters.
"We are not sure even about the number of the released detainees. We are expecting that more than 600 defendants were in jail and only some of these have been released since last night, including the 23 Shia activists," he told Al Jazeera
He said up to 200 may have been released since Tuesday night, and that those freed were political prisoners or "clerics who are normally active in political or human rights issues".
Shias account for about 70 per cent of the population, but are a minority in Bahrain's 40-seat parliament.
End item/ 129
