The ghosts in a dream represents the aspects of your inner self that are unknown even to yourself. Sometimes ghosts indicates the things that are no longer important to us, but we remember them from time to time. If someone has suddenly passed away, then it means you are thinking about those people in different way. It is very common and normal dream. The ghosts could also show the fears we have of unknown situations or something else.
Read more about dreaming of Ghosts in other dream meanings interpretations.