Why does a guy stare at a girl with a lingering look? mature answers only!?

well I am an average girl anyway I have this doubt that I need to clarified ? Recently I have caught this guy co-worker who by the way is married! Staring at me on various occasion first I began to think I was Imagining things ? Just recently he stared from the upstairs office he was alone and I has on the first floor, I was working and I felt that someone was looking at me? Sure enough I quickly looked up and there he was staring at me with lingering eyes with no expression on his face. Then I looked away so did and he went on about his bussiness. Soon after he was off for the day and call my name while leaving I was answering a business phone call? I didn't say anything and acted like nothing happen! I catch him staring at me often when he says hi he just seems space out? He likes to stare this is making uncomfortable and I don't want to tell anyone and create a drama or speculate things? I just want a guys perspective on this situation? Thanks alot . why does he does this it's creepy! he stares with no smile is he infatuated or what ?