I guess you need to define what is meant by "ghost" first. But as for asking if someone has actually travelled into the future: well I can guess the answers you may receive.
If you are to accept the concept of spirits that can be alive or dead, and time being something you can be 'outside of' once no longer part of the material world , then you can presumably accept that spirits could effectively wander to any time and put in an appearance.
I'm unsure what answer you were looking for, to be honest.