"Not because he's black," said Ellison, who is black, on Tuesday. "That's identity politics. I reject identity politics.
"He speaks with a unifying spirit," Ellison told about 100 employees at the Star Tribune newspaper during a lunch-hour event for Black History Month.
Ellison, a Democrat, is the first Muslim elected to Congress and the first black elected to Congress from Minnesota.
While Ellison is supporting Obama at this stage of the campaign, the congressman acknowledged that he may end up backing New York Sen. Hillary Rodham Clinton if she wins the Democratic nomination.