A system and a method are disclosed for authenticating a subsequent callback from a public safety answering point (PSAP) in response to a user agent's initial emergency call. In one embodiment, the user agent forwards a token to the PSAP during the initial call, and the PSAP returns the token during callback. The PSAP is authenticated when the forwarded and returned tokens match. In another embodiment, the user agent encrypts a token using a Public Key Infrastructure and forwards the encrypted token to the PSAP. The PSAP decrypts the token and, upon callback, includes a signed digital certificate based on the token. The user agent authenticates the PSAP when the decrypted digital certificate matches the originally sent token. In yet another embodiment, the user agent forwards a first token to the PSAP. Upon callback, the user agent forwards a second token to the PSAP. The PSAP performs a function on the pair of received tokens and forward the result to the user agent. The user agent performs the same function on the same tokens to obtain a local result. The user agent authenticates the PSAP when the local and forwarded results match.