I keep seeing a black figure but only on stairs?

I’ve been seeing this black figure in the corner of my eye every now and again and I don’t know if it’s nothin or something else? I’m not very knowledgable in the subject but I thought maybe it’s something more as I only ever see it on stairs. Whether I’m out or at home it only ever appears on the stairs and disappears whenever I double back and I’m not sure if I should be scared or if it’s nothing to be afraid of? Any help or info on the situation would be very very appreciated!!