During a trial in Tulsa, Betty Shelby, 43, said she had shot Terence Crutcher, 40, because she feared he was reaching for a gun in his car during a routine traffic matter last September.
Police video showed him with his hands up before he was shot.
The shooting added to a national debate about racial bias in the US police.
High-profile incidents involving African-Americans dying at the hands of police have led to demonstrations across the country in recent years.
A crowd gathered outside the courtroom after Wednesday's verdict, chanting "No justice, no peace, no racist police."
During the week-long trial, Betty Shelby denied race was a factor in the shooting.
Police later said Mr Crutcher failed to obey commands, and Ms Shelby testified that she had thought he was reaching for something in the car.
The police video showed Mr Crutcher walking away from officers, his hands in the air, before he was shot.
An officer was heard on a recording from a police helicopter calling him "a big dude" who was "probably on something".
In another video filmed inside a police car, Mr Crutcher was seen walking away from officers and toward his vehicle with his hands up before he approached the door on the driver's side.
There he dropped to the ground after a stun gun, and then a gun, were fired. He died later in hospital.
Mr Crutcher was found to be unarmed after the shooting.
A jury in the US state of Oklahoma has found a white policewoman not guilty of manslaughter over the fatal shooting of an unarmed black man last year.