Ugandan pop star-turned-MP Robert Kyagulanyi, known as Bobi Wine, was escorted home by police from the Entebbe International Airport.
He was allowed to speak atop a vehicle to the huge crowd of his supporters who were not allowed to meet him at the airport.
When he landed, security agents separated him from other passengers and took him away.
At the time, it was unclear where they were taking him.
Uganda's police chief, Martin Okoth Ochola, insisted that Mr Kyagulanyi "is not under arrest".
"What we have done is to escort him from Entebbe airport to his home," he told AFP.
"We are under obligation to provide security and this is what we are doing."
Mr Kyagulanyi had been in the US for medical care after alleged torture by security forces while in custody.
He has been charged with treason following campaign violence during a by-election in August. He denies the charge.
The Kyadondo East MP told a BBC reporter at his house that he had “come back to fight”.
-Reporting by Daily Monitor, BBC and AFP.