Although the justice minister, Malik Duhan al-Hasan, escaped unharmed, five of his bodyguards were killed on Saturday.
Witnesses said the assailant drove towards the convoy close to al-Hasan's home in Baghdad.
"There was a blast alongside the convoy. A booby-trapped car came alongside and blew up," said traffic policeman Husayn Abid.
At least five other cars were damaged in the explosion and hospital sources said at least eight people were wounded.
"We were working as painters near the ministry when suddenly there was an explosion. The glass shattered everywhere, hitting us," one of the wounded, Khalid Walid, said from his hospital bed.
The blast occurred in a district in the west of the capital just before 0900 (0500 GMT), officials said.
Also on Saturday, a cleric belonging to the Iraqi Islamic Party was assassinated in front of his home in Baghdad, said party officials.
Shaikh Abd al-Samad Ismail al-Adhami was gunned down by unidentified assailants. The motive of the attack is unclear.
In the central city of Samarra, the head of the Iraqi National Congress and his son were also killed when unidentified assailants fired rocket-propelled grenades at his home.
National Guard hit
In another car bomb attack, two members of Iraq's National Guard were killed and another 25 wounded in a blast in the town of Mahmudiya, 40km south of Baghdad, on Saturday morning.
A US military spokesperson confirmed the attack, but had no further details.
North of Baghdad, a roadside bomb in the town of Baiji killed a US soldier and wounded another. The death brought to 894 the number of US troops killed in Iraq since the war was launched last year.
An Aljazeera correspondent in Baghdad also reported two US trucks and a military wagon were damaged due to explosions on the main road in the Abu Ghraib area on Saturday morning.
Two Iraqis were killed.