A system and a method for dynamically unlocking a mobile device are provided. The method includes displaying various lock images, where at least one of the parts is altered, when an attempt is made to unlock the mobile device, determining whether a lock image, detected according to a user input, matches a preset image, and unlocking the mobile device according to the result of matching between the detected lock image and the preset image. The system and method increases the level of security when an unlock attempt is made in a public place.