A man sitting in a van outside a supermarket in Balgaddy, Lucan, was approached by two men who produced a suspected firearm and demanded cash at around 2pm.
They left the scene in a Ford Mondeo Car which was abandoned on Esker Lane a short time later.
Gardaí carried out a search of the area and two men were arrested.
They're being detained at Lucan Garda station.
Gardaí say they recovered the proceeds of the robbery, as well as a firearm.
