The attacker struck at a time when workers were arriving at their offices. It comes a week after militants stormed a National Directorate of Security (NDS) training centre in the Afghan capital.
Interior ministry spokesman Najib Danish told AFP six civilians in a car were killed when the attacker detonated himself.
"Six people were martyred and three others were wounded," Danish said.
"They were hit when they were passing the area in their Toyota sedan vehicle. We still do not know the target of the attack but it happened on the main road."
The health ministry confirmed the death toll but put the number of wounded at one.
The Islamic State group claimed responsibility for the attack.
"A martyrdom operation targeted a National Directorate of Security base... in the city of Kabul," its Amaq propaganda arm said.
An AFP reporter at the blast site said the attack happened outside the main entrance to an NDS compound. Security forces have swarmed the area, closing off the main road leading to the building.
Ambulances were seen leaving the scene, apparently taking casualties to hospitals in the city.
"Our initial information shows a blast took place near an intelligence headquarters in Shash Darak neighbourhood of Kabul," deputy interior ministry spokesman Nasrat Rahimi told AFP.
Kabul has become one of the deadliest places in the war-torn country for civilians.
Security in the city has been ramped up since May 31 when a massive truck bomb ripped through the diplomatic quarter, killing some 150 people and wounding around 400 others, mostly civilians.
Last week's attack on the NDS was also claimed by the Islamic State, which has expanded its presence in Afghanistan since it first appeared in the region in 2015.
It has scaled up its attacks in Kabul, including those on the country's Shiite minority.
The resurgent Taliban and increasingly IS are both stepping up their assaults on security installations and mosques.
On Friday, a suicide bomber drove an explosives-packed Humvee into a police compound in the southern province of Kandahar, killing at least six officers and destroying a building.
The Taliban claimed responsibility for the pre-dawn ambush.
Afghan forces, already beset by desertions and corruption, have seen casualties soar to what a US watchdog has described as "shockingly high" levels since NATO forces officially ended their combat mission in 2014 and began a training and support role.
Morale has been further eroded by long-running fears that the militants have insider help -- everything from infiltrators in the ranks to corrupt Afghan forces selling equipment to the Taliban.
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