Passengers on the plane captured the aftermath and said the woman didn't say anything before leaping to the ground.
One passenger, Cathy Cole, wrote on Facebook about the bizarre experience.
"We landed and waited for gate to open up as we were 30 minutes early.
"A lady opened emergency exit door, which she was seated next to and jumped off plane. Ran to terminal.
"We stopped short of gate waiting and she got to the exit door open and jumped off onto the tarmac!
"Several people said "we have a runner" before we knew door was open! Jeez! Sitting in plane with sister and all passengers. Waiting for police and FAA to board.
"Now it turns out she was in (New Orleans) at United desk. Paying cash to get on this flight. She sat in isle one row in front and across from me," Cole wrote on Facebook.
Another passenger took a video on board the plane with the emergency door missing.
It is unclear if the woman is still in Houston police custody.