Freedom was granted on the condition that they report regularly to police and remain within the districts where they live, the Abolish ISA Movement said in a statement late on Friday.
The Malaysian government jailed more than 200 suspect fighters between 2001 and 2003, but many have been released in batches over the past few years.
At Jemaah Islamiyah's peak in early 2000, it had members in several Southeast Asian nations, though officials say the group has been decimated in recent years in a Western-backed regional crackdown.
Among the strikes attributed to Jemaah Islamiyah and affiliate groups are the 2002 bombings on the Indonesian resort island of Bali that killed 202 people, mostly foreign tourists; the 2003 and 2004 attacks on the JW Marriott Hotel and the Australian Embassy in Jakarta; and the 2005 triple suicide bombings on restaurants in Bali.
The latest release is believed to be the third this year of suspects held under the ISA without trial.
Activists estimate a total of eight others were freed in June and August, but authorities did not publicly announce their release.
Internal security ministry officials could not immediately be contacted.
Authorities have said in some previous cases that suspects were freed after they repented following rehabilitation programmes and counselling that ISA detainees typically undergo.
Malaysian opposition and human-rights groups have repeatedly called for the ISA to be repealed, saying the law is abused to silence dissidents.
The government has said it is necessary to protect national security and ensure stability.