What do you do...

When you have a stong feeling that a girl you work with likes you, or is interested, but has a serious b/f? There's a girl I work with who ALWAYS smiles at me and talks to me when she passes me, always looks at me when I walk by, and also just so happens to leave her desk at the same time I do on more than a few occasions to make sure we leave the building at the same time. I mean it's obviously done on purpose.

We both have a mutual friend at work who tells me she has a serious b/f who says they've talked about getting married and all that noise. I've never acted on anything w/ her outside of an occasional fb comment, which she will do the same to me, especially w/ anything that could be descriptive about myself, as if she knows a lot about me. From what I do know about her, I like her and would totally go after her if she wasn't w/ someone.

I mean I repsect the fact that she has a b/f so I'm not like asking her out or anyhting but is this normal for something like this to happen? I mean it's not like we are good work friends or anything, and I keep to myself pretty much all the time, but when she does things like what she does, they are obvious.

It all depends on how reliable your radar is. If you have had a history of being correct in your assessment, then follow your instinct.
If you have been wrong more often than correct, then you have to obtain more information before you make a move.