Worshippers including Bali's governor, I Made Mangkupastika, made offerings and recited prayers at the temple inside a zone declared off-limits by disaster officials.
Bali is the only predominantly Hindu province in Indonesia, the world's most populous Muslim country. Warnings that the volcano could erupt anytime have caused 140,000 people to flee to safer areas.
Bali's religious leader, Gusti Ngurah Sudiana, said prayers were performed across the island by Hindus, Muslims and Christians.
Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said tremors from the volcano, which indicate rising magma, have remained at high levels since Agung's alert status was raised to the highest on September 22.
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Agung, about 70 kms to the northeast of the tourist hotspot of Kuta, is among more than 120 active volcanoes in Indonesia.
The exclusion zone around the mountain extends as far as 12 kms from the crater in places.
Another volcano, Mount Sinabung on Sumatra, has been erupting sporadically since 2010, sometimes blasting volcanic ash several kilometres into the air and forcing more than 30,000 to evacuate their villages.
Indonesia is located on the Pacific "Ring of Fire," an arc of volcanoes and fault lines encircling the Pacific Basin, and is prone to seismic upheaval.