Muhammad Ali said his client was detained for alleged involvement with a new militant network in Indonesia's westernmost province of Aceh.
Bashir is best known as the spiritual leader of Jemaah Islamiah, the al Qaida-linked terrorist group responsible for the 2002 Bali bombings that killed 202 people.
He spent several years in prison for his involvement with the group, but was released in 2006.
Mr Ali said Monday's arrest took place in West Java's Ciamis district.
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