KwaThema police spokesman Captain Mandla Phori says the owner of the firearm alleges that the weapon was under his pillow when his girlfriend entered the room.
According to Phori, the man further alleges that he left his girlfriend alone in the room, and when he came back, he noticed her hiding something under her dress.
Phori adds that the man looked for his firearm, but was unable to find it.
The stolen firearm was reported to KwaThema police, and a case was opened.
The man’s girlfriend was arrested at about 5pm, after the firearm was found in her possession.
She is expected to appear soon in the KwThema Magistrate Court.