What if I were to not tell my boss that he overpaid me?
Do you have a good reason for what you're doing?
He can afford it and I need the money.
You shouldn't lie about getting overpaid. He will eventually find out and you'll be in trouble with your boss.
Screw that! I'm not going to tell him. He'll never know.
Your boss will eventually find out that you received more money than you were supposed to and it's wrong not to tell him about it just so you can get some extra cash. If you value your job, you will come clean.