Police in Kisoro District have arrested Mr Mubarak Kirunda, the chairman of Central Division Local Council III in Jinja Municipality.
Mr Kirunda, a member of the Opposition Forum for Democratic Change, was arrested together with Mr Stephen Ssekanjako, a resident of Kamengo village, Mpigi District and Mr Gideon Neerugendo Nsabimana, of Mugo village in North Kivu Eastern Democratic Republic of Congo.
They were intercepted by security officials at Bunagana border on Wednesday while travelling to the DR Congo.
A detective at Kisoro Police Station who spoke on condition of anonymity to speak freely, says the trio failed to explain why they were crossing to DR Congo.
The detective says that security officials also questioned the travel documents which were produced by the suspects.
In a police statement, Mr Kirunda said that he was crossing to DR Congo to trade in fish.
Kisoro District Police Commander, Mr Charles Okotto says that the suspects are being detained at Kisoro Police Station for questioning.