Farah, who on Saturday was given a CBE in recognition of his golden year, even tried to produce his two medals from the London Games in an effort to prove he was not a security risk.
However, he was still questioned "on suspicion of being a terrorist" due to the fact he was born in Somalia.
“I couldn’t believe it," Farah told The Sun on Sunday. "Because of my Somali origin I get detained every time I come through US Customs.
"This time I even got my medals out to show who I am, but they wouldn’t have it.”
Farah was attempting to fly to Portland, Oregon, where he trains under the gaze of famous coach Alberto Salazar.
The 5,000m and 10,000m Olympic champion says it is not the first time he has encountered problems with US Customs, despite being one of the most famous athletes in the world.
"When we tried to get a residency visa, Nike obviously signed it all off and we thought it was going to be straightforward," he said of a previous incident.
“We were in Portland on a tourist visa so had to leave and re-enter the country as a resident. So we flew to Toronto to stay for a few days, then come back in.
“But when we were there we got a letter telling us we’re under investigation as a terrorist threat and we would have to stay away for 90 days."