A method generates an authentication key to be used in an authentication algorithm at position at which a mobile station's subscriber is located. First, when there is a request to create the authentication key by a customer service center (CSC), at an authentication center module (ACM), a first type of parameters are issued and transmitted to a mobile station (MS). At the MS, a reference key to be used in creating the authentication key is then obtained on the basis of the first type of parameters to send the reference key to the ACM. A second type of parameter is derived by using the first type of parameters when the reference key is received from the MS and then transmitted to the MS at the ACM. At the MS, the authentication key is generated by using the first type of parameters, the second type of parameter and the reference key and a key generation complete message is transferred to the ACM. In response to the key generation complete message from the MS, at the ACM, the authentication key is generated by using the reference key from the MS, one of the first type of parameters and the second type of parameter and a key generation complete message is transferred to the CSC to allow the MS to be activated so that the MS's subscriber can use a communications service provided by a mobile communications system.