Iraqi police say the bomb exploded in the capital's eastern Baladiyat neighborhood.
Insurgent bomb attacks have continued in the Iraqi capital despite a massive U.S. and Iraqi military crackdown since February aimed at ending violence there.
Al-Sistani Aide Killed
In Najaf, an aide to Grand Ayatollah Ali al-Sistani, Iraq's leading Shi'ite cleric, has been slain.
Police said that Sheikh Abdullah Falak, al-Sistani's legal adviser, was stabbed to death in his office on July 20.
His killer remains at large. Last month, another Sistani aide was shot dead in Najaf.