Yala provincial chief Major Itthipol Atchariyapradit led a team of explosive ordnance disposal (EOD) officials to the scene of the attack in Tambon Yaha.
The EOD officers found metal pieces of fish cans used to make the half-kilogram bomb, which was detonated by a timer.
The bomb was placed in a coffee bag and left at the scene.
The four men sustained slight wounds and were discharged from hospital after being treated.
Witnesses said they saw two persons on a motorcycle drop the coffee bag off at the scene. The driver wore white traditional Muslim clothes and a white crash helmet, while the person riding pillion wore black clothes.
After dropping the bag off, they lit a giant firecracker and threw it on the ground, witnesses said.
When a village head and other villagers went to inspect the scene five minutes later, the bomb went off and wounded them.
Officials believe the attack was the work of insurgents.