depends on what you call a ghost lol.
The one ghost I saw could float just above the ground, Ooooooo!!!
YES, THAT'S HIS SPIRIT>HE'S TIRED OF TELLING U TO CLEAN YOUR ROOM FOR THE PAST 2 YEARS
I for one believe you. "Ghosts" can move things around, hide things and make them reappear in an obvious spot afterwards, you actually can see them in the mirrors as forgottenangel said, they can bother you at night while you are trying to sleep, they can slam doors/cabinets/refrigerators open and shut, they can possess dolls and stuffed animals, they can physically hurt you and touch you, they can manifest themselves through sound, turn on stereos/tvs even speak from the television. I don't care if you think I'm crazy, I've seen my fair share of things, people and I have told eachother our stories, on plenty of occasions we haven't seen these things alone but with friends and family. Study up, some of these happenings that other people experience can be pretty darn scary. Oh and dogs and cats can sense them (maybe even see them), so can young children who have not yet been brainwashed by an unbelieving world.
Casper the Friendly Ghost used to play with live children, but your dearly departed father is not turning on your televisions.