Mills, who was born in Canberra to a Torres Strait Islander father and Aboriginal mother, was heckled as he lined up for a free throw in San Antonio’s 110-94 win in Cleveland on Sunday.
“Hey, Jamaican dog. They want their bobsledder back,” the spectator was heard to shout as Mills lined up his shot.
“Jamaica just called; they want their bobsledder back,” the fan added.
Mills later addressed the incident in a posting on Twitter.
“I am a proud Islander,” Mills wrote following the game.
“Like my Jamaican Brothers, me & my family in the islands of the Torres Strait have experienced racial slurs for decades. Hope your efforts will enlighten this confused, hateful fan.”
Mills, 29, has played for San Antonio since 2012. He has represented Australia at three Summer Olympics, 2008, 2012 and 2016.