System and method for authentication in a communications system

An authentication system and method in a communication system are provided. The authentication system includes an authenticator for receiving from a first Foreign Agent (FA) a location change notification notifying that an Mobile Station (MS) has moved to the service area of the first FA, after the MS completes initial access to a second FA using an authentication scheme with an Authorization, Authentication and Accounting (AAA) server in the service area of the second FA; and transmitting to the first FA a first key and a second key of the MS generated during the initial access of the MS in response to the location change notification.