Provided are a method of displaying an interface of a mobile device including a touch screen and a mobile device performing the method. The mobile device includes a touch screen having a first area and a second area. The method includes receiving, when the first and second areas are locked during a phone call state of the mobile device, an input function activation signal, and displaying, in the second area, an interface comprising a plurality of operation keys related to the phone call state, according to the received input function activation signal.