Ilham Djaya, chief warden of Bali's main prison, said: "Remissions were given to the Bali bombing convicts because they displayed good behaviour."
The jail term of six convicts jailed for helping to plan the 2002 bombings of two nightclubs in the Kuta tourist district, sheltering key suspects and setting up a website to support the attack were reduced by five months.
The other four were convicted of involvement in suicide attacks on restaurants in 2005, which killed 20 people. They had sentences cut by two months.
The Indoneian government says all prisoners have a constitutional right to sentence reductions, even convicted militants, except those serving life imprisonment or on death row.
Andi Matalatta, the Justice and Human Rights minister, said about 64,000 inmates had their jail terms reduced on Friday, most by a few months, while about 6,000 were freed.
Three others convicted for the Bali bombings – Amrozi, Imam Samudra and Ali Gufron – were sentenced to death over the attacks.
Their case is being reviewed by the supreme court.