Jackson said at a news conference Wednesday that he had said Obama's speeches can come off as speaking down to black people and that there were other important issues to be addressed in the community, such as unemployment, the mortgage crisis and the number of blacks in prison.
He said he was not aware the microphone was still on.
Jackson declined to repeat the comments, but said he decided to apologize publicly after hearing from Fox News that it would air them.
In an interview with The Associated Press earlier Wednesday, Jackson said he didn't remember his exact words, but said he was "very sorry."
The Fox News program "The O'Reilly Factor" aired Jackson's comment Wednesday night, including a slang reference to his wanting to cut off Obama's testicles. The report bleeped out the slang but made clear what Jackson said with subtitles.
Keep going, Obama! Without even raising a finger you're making them jump right off a cliff. All you have to do is make them feel the irrelevance they've represented for ages, just by being there.