"I just wanted to say hi to the president," Bush explained.
White House press secretary Jay Carney went over to the former president to introduce himself.
"I know who you are," Bush responded with a smile.
Bush, who was seated in a scooter, is the only living president who is not participating in this week's civil rights forum in Austin, presumably due to his health. Obama will deliver the keynote address at the event on Thursday, the 50th anniversary of the Civil Rights Act being signed into law.
In Houston, Obama will attend a closed-press roundtable discussion at a private home with around 30 donors who contributed up to $32,400 each to the Democratic National Committee.
Later in the evening, the president will headline a joint fundraiser for the Democratic Senatorial Campaign Committee and the Democratic Congressional Campaign Committee at the home of trial lawyer John Eddie Williams Jr. Tickets for the event range between $16,200 and $64,800.