Likely an office building related to activities at the North Ramp. Possibly for the Red Hats, a unit evaluating Russian fighters and other hardware.
Built between 08/2011 and 05/2012
8/2023: This building has a roof overhang on the south end. Possibly a loading dock or concealed hangar doors. It was built around he same time when the HH-60U "Ghost Hawks" were put in service at Area 51. Possibly a hangar/warehouse for the HH-60U fleet?