Broadcasters showed footage of cars and motorbikes driving away from Tangkuban Parahu on roads covered by ash.
The disaster mitigation agency said the tourism spot had been closed and the alert status of the volcano was being evaluated.
The volcano is about 30km north of Bandung, the capital of West Java province.
Indonesia is on the so-called Pacific Ring of Fire and has scores of active volcanoes, sometimes posing a threat to life and disrupting air travel, particularly on the most heavily populated islands like Java and Bali.
