Those detained were identified as Hemanta Chakma, 20, Tapan Chakma, 18, and Manas Chakma, 20.
Police raided the house of Kalasona Chakma around 1am on Thursday Jurachharhi Upazila Sadar and nabbed the three youths , said Jurachharhi Police Station OC Yusuf Siddiqui.
A light gun was also found on them, he said.
A case was filed against them under Arms Act, the OC added.