The quake originated along the Philippine Trench and was not linked to the magnitude-7.8 earthquake that struck Mindanao on June 8, with the epicentres more than 250km apart.
The 7.8-magnitude earthquake off Mindanao on Monday toppled buildings, triggered landslides and prompted tsunami warnings across parts of the southern island.
Andrie Yunus of the KontraS rights group suffered serious injuries when two men on a scooter threw acid at him in March, while he was riding a motorbike.