The motorcyclist was injured and taken to the hospital, said Katie McCormick Lelyveld, a spokeswoman for Michelle Obama.
None of the campaign staff in the vehicle with Mrs. Obama were hurt.
The vehicle was hit by the motorcycle as it attempted a left turn just south of Hampton, where Michelle Obama was due at a rally.
The Washington Post reports that the motorcyclist, 40-year-old Iowa Falls hydraulic mechanic Tim Emerson, landed on grass softened by three inches of weekend rain and lay still with a cut on his head.
"He got in a little bit of a hurry and tried to go around everybody," a friend of Emerson's riding another motorcycle told the Post. "I didn't believe he was going that way at an intersection. He went around two other cars that he shouldn't have."
Obama later told the crowd the event would be rescheduled.