The accident took place on the Dhaka-Aricha highway at 12 pm on Saturday, according to Riyad Mahmud, chief of the local highway police outpost.
The victims have been identified as Jahidul Islam, 40, Abdur Rahman, 25, and Abdur Razzak, 30.
They were returning home by autorickshaw after selling onions at Barongail market when a Paturia-bound bus of Comfort Line Paribahan hit their vehicle, Riyad said.
Jahidul and Rahman died on the spot and Razzak succumbed to his injuries on his way to Dhaka for better treatment from the local hospital, Riyad said.
Police detained the bus driver, Sattar Molla, 55.