An apparatus and a method for updating firmware by using a security integrated circuit in an electronic device. An electronic device may include a security integrated circuit (IC) providing a rich execution environment and a secure execution environment. The security integrated circuit includes a main processor operating in the rich execution environment and a secure processor operating in the secure execution environment. The secure processor is configured to perform user authentication based on firmware update information received from a server through the main processor. If the user authentication is successful, authentication information is generated corresponding to the firmware update information and stored in at least a part of a secure memory. If the firmware is installed, authentication of the firmware is performed based on the authentication information stored in the secure memory, and if the authentication of the firmware is successful, the firmware is installed.