The bomb, planted near a roadside tea stall in Landhi area of Karachi, killed the shop owner and a constable, officials said.
The device was triggered by remote control this evening, they said.
Two women were among the injured, who were taken to a nearby hospital.
No group claimed responsibility for the attack.
Karachi, Pakistan's largest city, has recently been rocked by a wave of sectarian, political and ethnic violence.