The car bomb went off in the Iraqi capital's Mansour neighbourhood leaving another 15 people wounded.
Meanwhile, a roadside bomb blast targeting a police patrol near Baghdad's University of Technology killed a policeman and a civilian. Another officer and six bystanders were wounded.
Gunmen also killed policeman in Baghdad, where fighters have carried out a series of large attacks despite a security crackdown since mid-June.
A separate bomb attack also killed Brigadier-General Ali Hassan Jubur, head of operations in Muqdadiya's police headquarters, police said.
Police have discovered three dead bodies in the ethnically mixed town of Diyala, which is increasingly becoming one of the most violent regions in Iraq.
Police have arrested a man following the killing of a police office in Kirkuk. They arrested him in a local hospital and his interrogation led to the arrest of another two policemen suspected of links with fighters, police said.
Police have also found 15-dead bodies in un-named locations.