King Hamad al-Khalifa, a Sunni Muslim, pardoned the 23, who are all Shia Muslims, in response to demands by the Shia-led opposition and massive rallies in Manama.
Among those released on Tuesday were a member of Committee for the Victims of Torture, Abdul-Ghani Khanjar, the human rights activist Ali Abdulemam, who runs bahrainonline.org and Mohammed Saeed, who works with the Bahrain Center for Human Rights.
"The 23 have been released," said MP Jassem Hussein, a member of the Islamic National Accord Association.
The detainees, along with two more who were being tried in absentia, faced charges of forming an illegal organisation, engaging in and financing terrorism and spreading false and misleading information.
Their release follows a pardon announced by King Hamad in response to this month's protests.
Sixty per cent of the Bahraini population is Shia but the monarchy is Sunni.