The three men lost their final appeal late last week and have said they will not seek clemency.
"My hope is it [the executions] could be done before the fasting month, but if it falls in the fasting month, we will discuss it more specifically," Hendarman Supandji, the attorney-general, said.
Hendarman said his office held documents signed by the men and their families waiving their right to a presidential pardon.
Amrozi, Mukhlas and Imam Samudra are being held at a maximum-security jail on Nusakambangan island off Central Java.
Indonesia has never revealed details of judicial executions in advance.
Abubakar Nataprawira, a spokesman for the national police, told Reuters they had prepared the firing squad for the execution.
"We are ready. Any time the attorney-general gives us the time and place of the execution, we have prepared for it."