He asked me to join, but I know I won't as as fas as I know Christians are not allowed to join, is it right?
Tell your friend, who is apparently new to all of this, that he shouldn't be asking you to join the Masons.
The Masons are not permitted to invite anyone to join their lodge. It is one of their rules that a prospective member must first approach a Mason and ask if he wants to join. Now, the Masonic friend can get around this by talking about how great the lodge is, how many friends he's made there, etc. But he can't *ask* you to join.
You should tell him this so he doesn't get into trouble with them later.