Human rights groups in Kenya say two activists who disappeared in neighbouring Uganda five weeks ago have turned up alive and well.

Eyewitnesses reported seeing Bob Njagi and Nicholas Oyoo being forced into a car by masked uniformed men after a political event where they were supporting the Ugandan opposition leader Bobi Wine.

On Saturday, activist organisation Vocal Africa confirmed the men were safe, and being transported from Busia in Uganda to Kenya's capital, Nairobi.

"Let this moment signal an important shift towards upholding the human rights of East Africans anywhere in East African Community," the organisation wrote on its Instagram page.

Ugandan police denied the men were in their custody, but Kenyan rights groups lobbied the Ugandan authorities to free them.