Mount Sinabung erupted in September after being dormant for 400 years, and increased eruptions in November led to mass evacuations within a 3-mile zone around the volcano.
The threat of renewed eruptions means 18,412 evacuees have little hope of returning home any time soon, officials said.
"The seismic activity of Sinabung is still high," the head of the National Volcanology Agency, Surono, told China's Xinhua news agency Thursday. "I have not found out whether it is part of Sinabung's activities to find new seismic balance and [become] stable or to erupt again."
Mount Sinabung, 8,016 feet high, is in the Karo district of North Sumatra and is one of 129 active volcanoes in Indonesia.
When the volcano sent a column of ash 23,000 feet in the sky in early November, authorities raised the threat alarm of the volcano to the highest level.