Do my cats see ghosts?

For over a year I moved already in an older house (a kind barn / farm). I actually feel quite well here. Still, I had in the beginning a strange, strange feeling when I entered the first floor (especially the room under the roof, where there is the bedroom). My cats started then from time to time, to behave "abnormally", ie, one could think they would "see" someone or something, and then act scared. Perhaps other cats or pet owners here know this phenomenon?

I'm curious what you think of them...

VIAHERE