Romney was flying from Omaha to Santa Monica, Calif., when an electrical fire filled the cabin with smoke, ABC News reported.
The wife of Republican presidential nominee Mitt Romney was traveling with four staff members, two Secret Service agents and three crew members.
No one was injured.
"Don't need any caffeine to wake me up now! #adventure," Romney campaign spokeswoman Sarah Haley tweeted after the landing.
"A HUGE thank you to the crew and first responders for keeping us safe today!" she wrote.
"We have an electrical issue here and we're going to declare an emergency," a man's voice was heard on a recording of a conversation with the flight tower at Denver International Airport. "We'll probably need assistance here. We got smoke in the cabin."
The Canadair Challenger 600 regional jet was surrounded by fire trucks upon landing, Haley said.
Romney campaign spokeswoman Andrea Saul said Mitt Romney spoke with his wife immediately after the landing.