The robbery occurred around 11:30 a.m. at the Shell station at 5630 Lee Highway, near the intersection of N. Kensington Street.
According to scanner traffic, the suspect is a white male wearing gray pants and a gray sweater, described as approximately six feet tall and in his 40s.
Early reports said he robbed the station at gunpoint with a semi-automatic weapon and stole $400 to $500. Police said he fled the scene on foot, traveling south on N. Kensington.
A K-9 unit was dispatched from Alexandria to help the search. Police also went to the Rivendell School, which is across the street from the station, to notify administrators about the situation.
No injuries were reported.
Earlier this morning an armed robbery was reported at the Giant supermarket at 2901 S. Glebe Road near Arlington Ridge, prompting administrators to secure the building at nearby Gunston Middle School, according to scanner traffic. So far police have not responded to a request for comment about the earlier robbery.