The condition of the victim is not known.
Witness Bryan Armstrong said it appeared the man was approaching the officer with a large rock when he was shot.
An officer told the man to "drop the rock and stop walking," but he continued to approach the officer slowly as people came through the terminal door unaware of what was happening, Armstrong told CNN.
Nine shots can be heard on a video Armstrong posted to Instagram. A woman is crying in the background of the video as someone screams, "Get down!"
After the sound of gunshots, a male voice can be heard shouting, "Stay down, stay down!"
Dallas police told CNN they had no immediate information on the circumstances surrounding the shooting.