look at the long term - there are many reasons for this move by your boss.
If it's a big company, if he can be your boss means that's something in him which he possess which others don't. So hang around for a few more months. He may just test you whether you are up to the job or not.
If it's just a SME, you may want to just look out for other jobs which able to pay you on what you are worth.
Plus many many other scenarios which me is too sleepy to type.
Leave it to other bros ba