In theory it shouldn't be, because this poses a security risk. In reality, tools like
aircrack-ng can collect parts of the WPA negotiation process (this is how information is collected to allow for cracking WPA). That said, WPA technology is designed such that you can't directly listen in on another machines' communications with the post. There are only certain breakdowns in this that don't require a significant amount of effort (and I'm not sure if there are any tools built for monitoring and cracking a computer's complete negotiation process off the air, although you could probably do this based on the information that
I'd think there's some way to do this at the AP, but I have no idea what that is.