I seem to have gained a roommate

Well, I have been sitting on the couch this afternoon doing a combination of computer stuff and TV watching. Well, while doing this, a little mouse popped out of my kicthen to say hi. I made a noise when I saw it and he turned and headed back in to the kitchen and has seemingly disappeared. I wonder how he got in. I hope I can catch him in a humane way before having to lay traps down, no need in killing any animals. Or maybe I should just get a couple of cats .... hmmmm ....