His brother said he left the Xinjiang prison on Thursday morning and was now at his father-in-law's home in Urumqi. Fellow activist and close friend Hu Jia told BBC Chinese that Mr Gao was seeking dental treatment in Urumqi, the region's capital.
Mr Gao, a prominent human rights lawyer, was arrested in early 2009. He was accused of inciting subversion. He was released briefly in 2010, and claimed he was tortured while in detention. Shortly after that he disappeared again.
State media subsequently said in 2011 he would be jailed for three years for violating probation rules.
Mr Hu told the BBC that Mr Gao is "having problems with his teeth" but is expected to head to his hometown in north Shaanxi province after having treatment.