My dog won’t go into one room and I stopped forcing him

My dog isn’t scared of anything. He runs into every room, jumps on everything, eats whatever he finds. But for some reason, he just won’t go into the guest bedroom. At first I didn’t think much of it. I tried calling him inside, even put his food there once. He came up to the door, looked inside… and just stood there. Then he slowly stepped back like he changed his mind. What made it uncomfortable was the way he was looking. Not at me… but somewhere behind me. I stopped trying after that. I don’t know what his issue is, but I’ve started avoiding that room too.