My screen turns black when loading, but if I move my mouse it turns normal

as titled said, it turns black when loading, I can tab out and it looks all normal. and when I tab back it's black again, and if I move my mouse continuously, it looks normal. I don't know if it is a bug or not, but I do want to know how to fix it. ps. it happens when I quit a game, the screen flash black for several times.