The traders were returning to their neighbourhood after buying vegetables from the wholesale market in Manikganj’s Jaagir.
The arrests were made early morning Thursday in Kotchandpur Upazila.
Local police OC Ahmed Kabir Chowdhury said that they raided a primary school at a village.
"Four Jamaat activists have been held with five crude bombs."
He said several others managed to escape sensing police's presence.
Those arrested have been identified as Abdus Sabur Khan, 50, Mizanur Rahman Dorji, 30, Nazrul Islam, 50, and Billal Hossain, 32.