The Syrian Human Rights Committee claims that the 11 have been held in the Sednaya prison near Damascus since May this year.
A spokesman for the Syrian Ministry of Information refused to comment on the allegations on Thursday.
They were arrested over a programme to clean up their hometown of Darayya, which involved encouraging their townspeople to stop smoking, especially American brands, and advising local civil servants to refrain from accepting bribes, the SHRC said.
The London-based group says that its sources in Syria claim that the detainees have been exposed to interrogation under conditions of psychological and physical torture, and to periods of solitary confinement.
Security authorities have compelled the Darayya detainees to sign pledges to give up their political activities as a pre-condition of release.
Democracy on trial
Meanwhile, a group of 14 "democracy activists" are to appear before a Damascus military court for intending to participate in a banned conference on an emergency law in force since 1963, the Association of Human Rights in Syria said on Thursday.
"These activists participated in a group discussion in (the northern town of) Aleppo where a conference on the emergency law was to take place," said a statement sent to AFP.
"(The trial is) a violation of the freedom of expression and the rights of association and taking part in public life"
Association of Human Rights in Syria
"Although the conference had been cancelled, they were arrested in August for one day before being released and brought before a criminal court in accordance with emergency law," it added.
The law, which is condemned by human rights groups, allows authorities to make arbitrary arrests and bans public gatherings. Suspects are also subject to indefinite periods of detention and the confiscation of property, with no recourse to other courts to seek justice.
Among the 14 called to appear before the military court in Aleppo on October 22 are members of banned political parties and human rights organisations.
The trial is "a violation of the freedom of expression and the rights of association and taking part in public life," the statement said.
The association called for the "prohibition of such arbitrary practices with regard to civil activists in Syria and an end to character trials before exceptional courts," such as state security courts.