One of the rights groups, the Committee for Defending Human Rights in Syria, deplored the raid aimed at disrupting a meeting being held at a public hall in the northern city of Aleppo.
In a statement, the group said the arrests were "illegal and a further indication of the retreat in respect for human rights in Syria."
Human Rights Association in Syria, the other group, said police later released seven of the people they had detained at the hall. The meeting was to hear a lecture to mark the 40th anniversary of the declaration of the emergency law in Syria.
Rights activists said the police closed roads leading to the hall before the raid.
They appealed to the interior minister to release all those still being detained.
Political activity is tightly controlled in Syria, where the Ba'ath party under the Assad family has held power since 1970.
Succeeding his father in 2000, President Bashar Assad initially took limited steps to ease state controls. He released many political prisoners and also allowed small political meetings.
But since 2001, Syria has witnessed a renewed clamp down on pro-democracy activists.