A 27-year-old man was robbed in Carey Street, Kettering, between 11.15am and 11.25am, on Saturday, November 16.
The victim was approached by a man who asked him to hand over his money. The victim felt threatened by this and handed over his money, at which point the offender ran off in the direction of Montague Street.
The offender was a white man, 5ft 8in to 5ft10ins, aged between 20 and 30, of medium build and was wearing medium to dark blue dark blue jeans, white trainers, a three-quarter length green jacket with a hood, which was up and a scarf covering his face.
Officers would like to speak to anyone who may have witnessed this incident or have any information regarding it.
Witnesses to this incident, or anyone with information, should call Northamptonshire Police on 101 - alternatively, information can be given anonymously to Crimestoppers on 0800 555 111.