The robbery happened just before noon at Chase Bank in the 10600 block of Kuykendahl Road.
According to the Montgomery County Sheriff's Office, the man entered the bank, approached the teller with a note and advised her they were being robbed.
The bank employee cooperated and the man fled the scene on foot with an undisclosed amount of money.
The man is described as 25-35 years old, 5 feet 8 inches to 5 feet 10 inches with a slender build.
He was wearing dark-rimmed sunglasses and a dark hooded sweatshirt with the hood up.
The man was last seen running south into a wooded area.
Anyone with information about this crime is urged to call MCSO at 936-760-5876 or Montgomery County Crime Stoppers.