I don't want to put any negative thoughts into your head, but this brings 5 things to my mind immediately:
1. He is lying about you at work, and he doesn't want them to meet you because he will be caught out.
2. He might be a little insecure, and he doesn't want you talking to anybody that he works with about him
3. He might have an ex that works there, and he wants to avoid you 2 coming into contact at any cost.
4. He might have had a fling/is having a fling with somebody there and he would hate for you to find out.
5. He has been lying about his life/situation at home, and by meeting you he again might get caught out
Please do not act on any of the points that I have given you. Consider the ones that you feel are the most logical, and do some research...
Good Luck Dear