Secret Service spokesman Max Milien said the man, who was not identified, was standing near a security entrance to the White House and got in the motorcade's way. The vehicle stopped briefly at the security gate and then entered the White House complex.
Milien says the man was later interviewed by a uniform division officer and became combative. He was charged with assault on a police officer and unlawful entry.
Romney came to the White House for lunch with Obama, their first meeting since the election.
A CNN video of the incident shows a man briefly heckling Romney near the passenger side of the SUV before the vehicle proceeded through the gates and onto the grounds of the White House.