Police said they arrested the 21 in a drive on a flat at a building in Dhania of Kadamtali on Wednesday evening.
Kadamtali Police Station OC MA Jalil said two other women were also taken to the police station from the flat.
The two said they had come to the flat on a visit. "We are checking their statement," the OC said.
He also said police raided the building owned by late Jamaat leader Moazzem Hossain following a tip-off that the pro-Jamaat students met there to 'discuss antigovernment activities'.
Police could not confirm the names and posts of the Chhatri Sangstha members. "We are working on the issue," OC Jalil said.
