Bahri, a Yemeni national, passed away on Saturday in a hospital in the southern city of Mukalla, the BBC reported, quoting medical sources in Yemen as saying.
He is believed to have been in his 40s.
Bahri, also known as Abu Jandal, was also a driver for the late al-Qaeda leader, when he was in Afghanistan.
Bahri was freed from the US military prison in Guantanamo Bay and returned to Yemen in 2008.
He was involved in attacks by Islamist militants in Bosnia, Somalia and Afghanistan during the 1990s, but later renounced al-Qaeda.