“For him to be let out, it’s laughable,” he told Australian national broadcaster ABC.
Indonesian authorities said they believed Patek had rehabilitated himself inside prison after completing a deradicalisation programme.
Patek has said he wanted to devote himself to deradicalising other inmates.
Australia’s deputy prime minister Richard Marles urged Indonesia to keep Patek under “constant surveillance”.
“We will continue to make representations to make sure that there is constant surveillance of Umar Patek,” he told ABC.
“I think this is going to be a very difficult day for many Australians.”
Australian Prime Minister Anthony Albanese in August said he had nothing but “contempt” for Patek’s actions and that his early release would be traumatic for victims’ grieving families.
Hundreds of mourners and survivors gathered in Bali and Australia in October to mark the 20th anniversary of Southeast Asia’s deadliest terror attack.