Provided are a wireless x-ray detector for automatic exposure detection and a method of driving the x-ray detector. The wireless x-ray detector includes: a first detection unit for detecting an x-ray incident in the x-ray detector; a second detection unit for detecting an x-ray that has passed through the first detection unit; and a gate driving unit for applying a gate pulse for controlling a switching device of the first detection unit, to the first detection unit, according to whether the second detection unit detects the x-ray that has passed through the first detection unit.