Had something similar at my grandparents place growing up, top of the stairs same as you. Always assumed it was sleep stuff playing tricks but it happened when I was wide awake a couple of times and that's harder to explain away.
The thing that got me was it wasn't threatening exactly, just stood there. No real shape to it beyond vaguely human. My cousin saw it too on a separate occasion without knowing I had, and described basically the same thing. That's the part that always stuck with me.
What did yours look like and what time of night was it? Curious if theres a pattern to when people see these things.