Police officials said a pickup truck exploded at night at the entrance of a wholesale fruit and vegetable market in the city of Samarra, 95 kilometres north of the capital.
They said at least 35 people were wounded and that several shops were damaged in the attack.
More than 5,000 people have been killed in Iraq since attacks began accelerating in April following a deadly security crackdown against a Sunni protest camp in the northern town of Hawija.
Places such as markets, cafes and mosques have been favourite targets for Sunni insurgents who aim at undermining the Shiite-led government in Baghdad.
Medical officials in nearby hospital confirmed the casualty figures. All officials provided details of the violence on condition of anonymity as they were not authorised to release the information.