The blast - described by the military as a terrorist attack - went off at a checkpoint at the northern entrance to Tikrit, 150 km (95 miles) north of Baghdad, Reuters reported.
No group has claimed responsibility for the car bomb attack yet.
In recent months, Iraq has been hit by a wave of bomb attacks, mostly claimed by Daesh (ISIL or ISIS).
In November last year, Iraqi forces captured the border town of Rawa, the last remaining town under Daesh control, marking the collapse of the terror group’s self-proclaimed caliphate in Iraq.
However, remnants of the group continue to carry out terrorist attacks in different parts of the country.