Qassim al-Moussawi says the explosion on Monday afternoon also wounded two people.
An Iraqi security official says one of the wounded is an Iraqi lawmaker who was getting into his car at the time of the blast. The official spoke on condition of anonymity because he was not authorized to speak to the media.
Al-Moussawi says he doesn't know if the blast was from a car bomb or a sticky bomb attached to a vehicle, or from rocket shot into the Green Zone.
The Green Zone is home to the U.S. Embassy, the Iraqi Prime Minister's office and the parliament.