The double gold medal winner, who was awarded a CBE in the New Year's honours list, said he was hauled before guards while entering the country for a holiday this Christmas.
The 29-year-old runner told 'The Sun' that border guards questioned him because of his 'Somalia origin'.
The athlete even resorted to showing his Olympic medals in an effort to prove who he was.
Farah said that he gets detained every time he enters the US because of his 'Somali origin'. He said that he was pulled aside by officials while visiting Portland, Oregon, with his family this Christmas.
He said on a previous visit to the country, he was asked to leave before receiving a letter explaining that he was 'under investigation as a terrorist threat'.
Farah moved to the UK with his British-born father when aged only eight.
"I couldn't believe it. Because of my Somali origin I get detained every time I come through US Customs," he said.
Farah, whose triumphs in the 5,000 metre and 10,000 metre races provided two of the most exciting moments of London 2012, trains in the US.
After failing to qualify for the 2008 Olympics, he moved his wife Tania and daughter Rihanna to Portland to work with legendary coach Alberto Salazar at Nike's headquarters.
But the runner said that he had previously encountered problems with border officials.
Assuming that his sponsors Nike had sorted out his residency visa, Farah 'had to leave' America as he was using a tourist visa.
"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 were under investigation as a terrorist threat and we would have to stay away for another 90 days," he said.
Farah claimed that his American coach had a 'friend who works for the FBI' who was a 'massive running fan'. According to the athlete, the contact 'got it sorted'.
