The hold up happened at a shop in the Scotch Quarter area of Carrickfergus on Saturday evening.
Police say that at around 8.50 pm, two men wearing masks and dark clothing entered the newsagents.
One of the men was armed with a suspected firearm.
They made off on foot with a sum of money and some tobacco and headed in the direction of Taylors Avenue.
No-one was injured in the incident.
Detective Constable Loreen Glenn said: “I would appeal to anyone who saw any suspicious activity in the area, or anyone who knows anything about this armed robbery, to contact detectives at Ballymena Police Station on the non emergency number 101.
“Or if someone would prefer to provide information without giving their details, they can contact the independent charity Crimestoppers and speak to them anonymously on 0800 555 111.”