Obama paused by a statue of King in the Capitol Rotunda after a luncheon hosted by members of Congress. He was accompanied by his wife, Michelle, and Vice President Joe Biden and his wife, Jill.
"You know this is the first time I have seen this," he said.
The King bust— a bronze sculpture 36 inches high on a 66-inch high Belgian black marble base—has been in the Capitol Rotunda since 1986, according to the Architect of the Capitol.
King's Bible was one of two Obama used for the ceremonial inauguration.
"I had the great privilege that the Bible we used was his Bible and they asked for it to be inscribed," Obama said. The other Bible belonged to President Abraham Lincoln.
Monday was the federal celebration of King's birthday.