A senior Somali police officer, Mohamad Duale,said: “The car exploded as it was closing on a base of Burundian peacekeepers.
The driver was killed and two civilians nearby were slightly injured.
“We are still investigating where the attack was aimed at – fortunately it did not hit any target.”
Witnesses said the car slowed down as it approached the base.
Extremist al-Qaeda allied Shebab gunmen have been fighting to topple the weak Western-backed Somali government in Mogadishu, where the administration survives under the protection of the 10 000-strong AU force.
Somalia has had no effective government since 1991 and in recent years the al-shabaab rebels and other groups have taken an increasing hold on large parts of the country.
Most of the insurgents last year left fixed defences in Mogadishu and switched to guerrilla and suicide attacks.
In early February a suicide bomber killed at least 15 people in a bar near the presidency.