Hie! i am 23yr old girl n currently workin...and there's this guy who's been staring at me , n that too?

intense stare for the last two three months...n he looks at my eyes..directly n doesnt hide away from starin till i do...he doesnt smile ...n his intense stare gets me..now the thing i am worried about is i find him attractive but he;s not making any move...i mean fr example while we passed each other on stairs all he did was stare n i smiled..and it goes on like this ...so what do you think...should i keep my interest in him?? how much should i wait..n makin first move from my side is difficult due to work environment//// P.S. that guy works in the office next to mine so we occasionly meet...