Court papers filed by Tulsa County said Officer Betty Shelby escalated the situation and over-reacted in shooting Terence Crutcher, 40. If convicted, she faces at least four year in prison, lawyers said.
The incident, captured on widely broadcast police videos, is one in a series that has raised questions of racial bias in U.S. policing.
"Although she is charged, she is presumed innocent until a judge or jury determines otherwise," Tulsa County District Attorney Steve Kunzweiler told reporters after an investigation in which more than 50 witnesses were questioned.
"I don't know why things happen in this world the way they do," he said.
Crutcher can be seen in two videos provided by Tulsa police on Monday with his hands in the air shortly before he was shot.
Shelby told investigators "that she was in fear for her life and thought Crutcher was going to kill her," according to an arrest affidavit.
An officer flanking her deployed a Taser on Crutcher, who was standing facing his vehicle. Then Shelby fired at Crutcher, whose left hand was not clearly in view, the affidavit said.
Shelby said she was traveling to another call when she came upon Crutcher. She said he did not respond to her questions and did not respond to her commands to stop as he walked to his vehicle with his hands in the air, it said.
"Officer Shelby acted unreasonably by escalating the situation," the affidavit reads, adding that "she became emotionally involved to the point that she over-reacted."
Tulsa police have said Crutcher was unarmed and there was no weapon in the vehicle. In a bid for transparency, they released the videos, one of which was taken from a police helicopter and the other from a dashboard camera in a patrol car.
The U.S. Justice Department has launched a separate investigation to see if the officers on the scene violated Crutcher's civil rights.