Dead people who appear alive in dreams have three general categories of participation: cameo, resolution, and judgment.
Cameo participation is a little eerie in recall, but not particularly noteworthy in the dream itself. In these cases, the dreamer simply sees a dead person intact and living, just hanging out in the dream scene. Often there is little direct participation in the dream per se. The dream image probably is tied to an activity that the dreamer and dead person once participated in together. Most likely, there is a latent sense of missing the person that made the dream appearance possible.
Resolution participation usually involves a specific action with the dead person. In this case, the dead person's presence is central to the unfolding storyline. Either you lack something they need or they act in a way to provoke emotion (positive or negative) from you. In either case, the transaction or inability to complete it revolves around some deficit that needs resolution in the relationship. These dreams may carry a sense of judgment or joy, depending on whether or not the relationship transaction is resolved. Judgment can often involve the dead person as a dead person or zombie. These dreams are particularly troubling as we often see ourselves as unable to reverse of complete the necessary actions to salvage a situation.
What traits did the deceased embody during their lives (i.e. Uncle John was a saint; Aunt Agnes was mean as a snake)?
Was their behavior in the dream consistent with or contrary to their general behavior in life? Perhaps you need to look more closely at the true personality of the deceased and how they were characterized by others.