The crude explosive, made of incendiary chemicals with a blasting device, went off in the compound of the DepEds division office in nearby Sultan Kudarat town in Maguindanao at about 8 a.m. Monday, shattering glass windows.
The blast came just a week after explosive experts defused an improvised bomb found in the premises of the DepEds Autonomous Region in Muslim Mindanao office here.
"It was not meant to harm. It was only part of the harassment of the education department," said Udtog Kawit, the provincial education chief.
Police say they have no suspects.
Local military chief Col. Essel Soriano said the latest bomb was not believed to be related to the spate of previous bomb attempts in Cotabato City and Manila because it used a different explosive and no group had claimed to have planted it.
In earlier incidents, the planted bombs used mortar shells or grenades but were not wired to go off.
These bomb scares were claimed by obscure organizations that said they were seeking a federal state for tribal groups.
However, authorities believe this is merely a cover for a group with another agenda. John Unson, AFP