Brittany Carter, 23, is accused of performing a sex act on the 29-year-old driver while Corey Jackson, 20, allegedly held a knife to his throat.
Police said the pair then stole $32 (£26) from the victim before fleeing the scene in the city of Findlay.
"We don't know why she did it," police Lt Robert Ring said.
"Maybe it was a distraction because they took money from him."
The assault unfolded after Ms Carter called the Trinity Express Cab Service in the early hours of 28 January, according to police.
