Mount Sinabung's activity has increased since last year and the alert for the volcano in North Sumatra province has been placed at the second-highest level.
No casualties were reported, but an official had earlier urged people to stay at least 3 km from the crater, Indonesia's Volcanology and Geological Hazard Mitigation Centre said.
Videos on social media showed little panic among residents over the eruption, which sent a column of white ash into the blue sky.
Wirda Br Sitepu, a 20-year-old resident, told Reuters that the situation had calmed and said "the mountain is not erupting, and the ash has decreased."
Indonesia straddles the so-called "Pacific Ring of Fire," a highly seismically active zone, where different plates on the earth's crust meet and create a large number of earthquakes and volcanoes.
Sinabung had been inactive for centuries before it erupted again in 2010.