The remote-control device, hidden near a police security checkpoint, went off at around 7 pm yesterday in Sai Buri district of Pattani province.
Thailand's three Muslim-majority southernmost provinces are in the grip of a decade-long insurgency which has seen more than 6,000 people killed -- the majority of them civilians.
Officials in the region are on heightened alert ahead of the 10th anniversary of a raid on a mosque in Pattani that left 32 insurgents dead, said Paradorn Pattanatabut, a security adviser to Prime Minister Yingluck Shinawatra.
Peace talks with insurgents representing some of the main groups have stalled amid a six-month political crisis in Bangkok.
"The suspension of the peace dialogue has made them exploit the situation and the weakness of the government because of the protests," Paradorn said.
Many local Malay-Muslim accuse the authorities of widespread human rights abuses and a lack of respect for their religion, culture and language. The militants have demanded a level of autonomy from Thailand.