Officials say the arrests were made on Friday in the town of Netrokona, the site of Thursday's blast. No other details were immediately available.
Authorities say the suicide bomber struck as police were defusing another bomb found in a building. They say casualties were high because hundreds of people had gathered to watch the police at work.
No one has claimed responsibility for the blast. But authorities blame the outlawed Islamic militant group, Jumatul Mujahedin Bangladesh, which wants to impose strict Islamic law in the Muslim-majority, but secular, country.