The bomb, detonated by a remote control device, was planted on a motorcycle parked near a busy vegetable market in Sibi -- a small town in the resource-rich Balochistan province, bordering Afghanistan, police said.
A police official in provincial capital Quetta said one person was killed and 24 others injured in the attack.
The blast also damaged motorcycles, shops and a vehicle parked nearby.
"It is a busy marketplace at this time of the day as traders come here daily for business. At the time of the blast it was crowded," police officer Ahmed Jamal said.
Jamal said no one had claimed responsibility for the attack but but Taliban militants and local Baloch separatist often carryout such attacks.
Security forces have cordoned off the blast site and a manhunt has been launched.