The toll increased with the deaths at Kenyatta National Hospital of three victims who had been hospitalized.
Police said they suspect the bomb on the bus in the Nairobi suburb of Eastleigh was detonated by remote control, the Kenya Broadcasting Corp. reported Monday.
Officials said at least 26 people, including at least one child and a suspect in the bombing, were injured, some critically.
Twenty-one people were treated and released.
Witnesses said they saw a man, apparently the suspect, jump from the minibus just before the explosion and he tried to get into a waiting vehicle before passersby detained him.
One witness, Mohammed Qadar Gudle, told Voice of America he felt the blast more than 500 yards away.
"I saw it, even the land was shaking," Gudle said. "I thought it was an earthquake. So once I saw [the vehicle] burning out, I ran to the near of it, and I saw almost seven people died and at least 25 injured, badly injured."
The explosion followed several grenade attacks across Kenya that officials blamed on Somali militants and their supporters, Voice of America said. The Somali militant group al-Shabaab has vowed to attack Kenya because Kenyan military forces entered Somalia in 2011 to battle al-Shabaab.