"I'm for Mitt Romney," the former president said as the doors of the elevator he was riding closed, according to ABC News.
Romney later called Bush to thank him for his support, the network reported.
Bush's last high-profile visit to the White House was an event with former President Clinton in January of 2010. The pair joined Obama in advocating for donations and support in the wake of the Haiti earthquake.
Since then, Bush has kept a relatively low profile, emerging only occasionally for charity causes.