The unnamed man reached into an open window of the vehicle as it stopped at a White House gate Wednesday. He was yelling Romney's name as he was taken away, CNN reported.
The Secret Service said in a statement the man "became combative with uniformed Secret Service agents and was arrested for assault of a police officer and unlawful entrance."
Romney was visiting the White House for a lunch with President Barack Obama, and did not appear to have been touched by the suspect, CNN said.
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'
Couple mistakenly served bag of cash at McDonald's drive-thru