During the first quarter of Game 3 of the Eastern Conference finals in Miami Sunday, a second foul sent Noah to the bench, where cameras caught him turning to the crowd and making the remark, the Chicago Tribune reported.
"I got caught up," Noah said. "A fan said something. And I said something back. I apologize."
The NBA's official release didn't specify what the fine was for, but the Tribune reported it was for the anti-gay slur.
The Los Angeles Lakers' Kobe Bryant was fined $100,000 for using the same slur against a referee during the regular season and was strongly rebuked by the league's commissioner, David Stern.
"I don't mean no disrespect to anybody. I just got caught up," Noah said.
The NBA is conducting a public-service ad campaign in which the league draws a line at trash talk that includes anti-gay slurs.