The woman was taking part in an act in which a crossbowman fired an arrow at her, the Swedish news agency TT reported.
She was supposed to move out of the way before being shot, but something went wrong and she was hit by the arrow in her stomach.
"Something went wrong in their communication," explained circus director Robert Bronett. "He aimed correctly but something went wrong."
Bronett said that the crossbowman was "shocked" and "devastated" by the mishap.
Fortunately, the woman was not seriously injured, Bronett said. She was able to walk and lay down on a stretcher without assistance after an ambulance arrived.