A Jakarta High Court official said on Monday that judges had rejected the appeal filed by Bashir after that verdict, but gave no details on the ruling.
Lawyers for Bashir, who the United States and Australia allege is the spiritual head of the al-Qaida-linked Jemaah Islamiyah group, said they had yet to be informed of the decision, but would appeal to the Supreme Court.
Bashir was convicted in March of conspiracy in the Bali bombings, which killed 202 people, but was cleared of the more serious charge of planning the 2003 attack on the US-owned JW Marriott hotel in Jakarta that killed 12 people.
His 30-month sentence was decried by the governments of the US and Australia, which were hoping for a longer punishment.
The conspiracy conviction relates to allegations that Amrozi bin Nurhasyim, who was convicted with more than 30 other men in connection with the Bali bombings, visited Bashir three months before the attacks to ask for his blessing.
Amrozi did not testify during the trial, and prosecutors based that part of their case on what police alleged he told them about the meeting. Bashir denied that the exchange ever occurred.
"This decision is naked cheating because our key witness, Amrozi, never testified at Bashir's trial," said Bashir's lawyer.