The Nimat Kada eatery on the Prince Road in capital Quetta was packed with people when it was attacked by unknown militants.
City Police Officer Abdul Razzaq Cheema said that one person was killed and 15 others injured in the attack.
"Police is searching for the attackers who fled after hurling the grenade," he said.
The victims were shifted to the Civil Hospital in Quetta for medical treatment, where condition of some of them was critical.
The Baloch are struggling for greater control over natural resources of the province which has seen a long-running insurgency.