Pentagon police spokesman Chris Layman says the person was taken into custody early Friday and that one or two other people may be involved. Layman says the car is in bushes near the Pentagon's north parking lot.
No other details about the investigation were immediately available.
The investigation has caused road closures near the Pentagon.
In another incident earlier this week, a motorist found with a gun and what appeared to be a suspicious package near the Pentagon was taken into custody.