Local police said the explosions occurred in a Muslim-majority residential area.
Two suspects were arrested but their identities and the motive behind the attack were still under investigation.
Mindanao is the homeland of the Muslim minority in the Philippines. Islamic rebels in the country conducted armed campaigns claiming breakaway in the southern Philippines since 1970s. Statistics showed that fighting has left over 120,000 people dead.
Major rebel groups have been in peace talks with the Philippine Government but other smaller extremist gangs that have pledged allegiance to the proclaimed Islamic State (IS) have still carried out bombings and kidnappings.-VNA