In general, seeing ghosts in your dream symbolizes aspects of yourself that you fear.
This may involve a painful memory, guilt, or some repressed thoughts. You may be anxious about your ability to achieve something in real life. Or, you may be afraid of death and dying.
If you were frightened by the ghost or it spoke to you, this is a warning that some powerful pressure will be put on you to join in a scheme or activity which is against your principles. Resist the temptation with all your strength, and if necessary get help from a trusted friend or adviser.
If you dreamed of being a ghost, this symbolizes a feeling of disconnection from life and society.
This dream may be a calling for you to move on and abandon your outdated modes of thinking and behavior, and make a positive change in attitude.