A bomber blew himself up near a security checkpoint in central Baquba city, killing four and injuring 18 others, police captain Haib al-Shemari told Anadolu Agency.
He said Iraqi troops sealed off all routes leading to the main governor's office in the city in anticipation of other attacks.
There was no claim of responsibility for the bombing.
Iraq is currently engaged in a wide-scale offensive to dislodge Daesh from Mosul, the last stronghold of the terrorist organization in northern Iraq.
In 2014, Daesh overran vast swathes of territory in northern and western Iraq, but Iraqi forces have managed to recapture most territory ever since.
