The bomber blew himself up as al-Zubayi, one of two deputies to Nuri al-Maliki, the Iraqi prime minister, and other worshippers were leaving a mosque in the courtyard of his house, according to police.
Five of al-Zubayi's bodyguards were killed in the blast while Mufeed Abdul-Zahra, an advisor, was wounded in the attack and died later at the hospital.
The attack came a day after a rocket landed in the Green Zone as Ban Ki-moon, the UN secretary general, and al-Maliki were holding a joint press conference.
Mahmud Othman, a Kurdish member of parliament, said Zubayi was al-Maliki's deputy on a ministerial committee for security, which was enough to make him "an important target".
But Imad Shahib, an Iraqi journalist, told Al Jazeera al-Zubayi was probably targeted simply "because he's part of the government and everyone here in Iraq is targeted".