The attacker, with explosives strapped to his body, struck outside the Ghocha Park mosque in the northern town of Sheberghan, where Dustum had been saying open-air prayers for the Eid al-Adha Muslim festival on Thursday.
"After the holy Eid prayer, as I left the mosque and I was putting on my shoes there was a big explosion. I am not hurt but at least 21 of our compatriots were injured," Dustum told provincial Aina Television station.
"According to the latest report I was given, six of them are in a critical condition."
Dustum blamed al-Qaida for the attack, without giving evidence to back his claim. "The investigation has not been completed but personally I think this was the work of terrorists and an al-Qaida group," he said.
Dustum, an ethnic Uzbek and former Afghan army general, was an unsuccessful candidate in last October's presidential election, won by Hamid Karzai. He won 10% of the vote, largely among the Uzbek and Turkmen minorities.
Television footage showed a group of people talking in the mosque's courtyard, followed by a blast and a cloud of smoke and scenes of panic. It then cut to a body and a charred pile of clothes lying on the ground.
Dustum's brother Qadir, who was injured in the blast, said Dustum's bodyguards stepped in front of the bomber and took the brunt of the explosion. "Two of the bodyguards are seriously injured," he added.
The exact number of injuries remained unclear. Interior ministry spokesman Lutfullah Mashal said 23 people were injured while local television journalist Muhammad Yusuf Rawanyar said 22 were hurt.
Dustum's militia is disarming as
part of a UN-backed scheme
Despite the attack, a visibly shaken Dustum continued to hold court on Thursday afternoon at his house in Sheberghan, receiving over 30 guests.
Visitors were frisked by a contingent of more than 10 armed guards at the gate of Dustum's compound but the former general only had two guards at his side.
One of Afghanistan's most feared military regional commanders, Dustum recently began disarming his local militia as part of a UN-backed scheme but was allowed to retain a personal retinue of 200 bodyguards.
Although he said his own forces had been weakened, he told the television station he would "continue to fight terrorism till the last minute".
Dustum - a nickname meaning everybody's friend - gained a reputation as a flinty maverick during the years of violence that have shattered Afghanistan.
He started out in the 1980s fighting for the Soviet Union against Afghan mujahidin commanders and then backed communist president Najibullah after the Russians left.
Dustum (L) ran and lost against
Karzai in the October election
During the civil war that followed the fall of Najibullah, he switched sides twice, first backing late resistance leader Ahmad Shah Masood and then going over to rival commander Gulbuddin Hekmatyar.
Dustum retreated to northern Afghanistan and built a fiefdom in the city of Mazar-i-Sharif, after battling with the Taliban for control of the city in 1997 in a brutal campaign marked by massacres of retreating troops.
Since the fall of the Taliban regime, Dustum has backed the government in Kabul, but he keeps control of substantial oil and gas reserves in the north.