"I received the decision letter this morning saying Gao Zhisheng is in Shaya prison in Xinjiang," his brother, Gao Zhiyi, told AFP. He added the document was issued by a Beijing court.
The official Xinhua news agency said last month that Mr Gao had been sent back to prison after a court ruled he had violated the terms of his probation, though it gave no date.
A Beijing court sent him back to jail for three years after ruling he had "seriously violated probation rules a number of times," the report said.
Bob Fu, head of Texas-based rights group China Aid, likened the jailing to internal exile.
"The Chinese government can use this remote jail to prevent concerned people to visit attorney Gao," he said in a statement.
The case has drawn the attention of both the United States government and the United Nations.
In December last year, the United States urged China to "immediately release" Gao and to clarify his whereabouts.
Days later, UN officials also called on China to release Mr Gao after state media said he had been sent back to prison for three years.