Can computer make a mistake if yes why if no why?

For the most part, computers do not make mistakes. They generally output answers based on the input given. If the input is wrong, the output can be wrong. In tech terms, we call this "GIGO" -- Garbage in, garbage out.

FWIW, Intel once made a CPU chip that had a floating point math error. For most calculations, it would have meant no errors. However, for very complex programs, the computer would definitely make a mistake with that particular processor on board.