No evacuation orders have so far been issued, and no casualties reported.
The National Disaster Mitigation Agency (NDMA) warned villagers living on the mountain's slopes to be alert for ongoing volcanic activity.
Footage showed ash from the 3,676m (12,060ft) volcano looming over homes.
Indonesia sits on the Pacific "Ring of Fire" where tectonic plates collide, causing frequent volcanic activity as well as earthquakes.
Semeru - also known as "The Great Mountain" - is the highest volcano in Java and one of the most active. It is also one of Indonesia's most popular tourist hiking destinations.
The volcano previously erupted in December, when about 550 people were evacuated.