Is it possible for me to have a ghost in my house?

I have been experiencing a lot of ghostly activity lately. I have heard footsteps upstairs whilst I have been downstairs, I have had the feeling of being watched all the time also. I hear noises when home alone, and when home alone only! I have asked this question a lot of times on this account but I need to know truthfully whether there is a possibility I have something paranormal in my house?