The robbery occurred around 23:50 on Trinity Road, at the junction of Dongola Road.
Police said the pair of 17-year-olds had been walking along the road when they came across two other boys.
One of the opposing pair was alleged to have threatened them with a knife, forcing them to hand over money and a mobile phone.
Pictured: The mugging happened where Dongola Road and Trinity Road meet.
A 17-year-old was later arrested on suspicion of the mugging offence, and remains in custody.
Anyone with information or who saw what happened is urged to call Police on 612612 or make an anonymous report via Crimestoppers by calling 0800 555111 or using their online form.