Why do computer accounts attempt to connect to wireless network?

I am getting warnings in my event log of computer accounts attempting to connect to the IAS server after the user logs off. So a log might show that JSmith succesfully connected to IAS. And then once he logs off, it will show his actual computer, lets say ABC, is denied access; because only users are part of our Wireless Users security group.

I just want to know why the computer tries to connect and if there is any security issue in allowing the computer to connect?