Omaha Police say the hold up happened around 12:40 Wednesday afternoon at the U-S Bank branch inside the Woodmen Tower.
Witnesses told police that the man walked into the bank from the west, approached the counter and handed the clerk a note.
After getting the money, the man left through the east doors and walked north on 17th Street. Police say no weapon was shown.
The suspect is described as a slender black man in his 40's. Omaha Crime Stoppers is offering a reward for information that leads to an arrest.
An additional $25,000 reward leading to the arrest of any suspect involved in the robbery of a bank is made possible by the local Bankers association.