An all in one (AIO) computer implemented as a personal computer (PC) or a display includes a high definition multimedia interface, a speaker, and a speaker control circuit. The speaker control circuit includes an earphone interface circuit, a main controller, a signal processing unit, and a signal control circuit. The earphone interface circuit detects whether an earphone is inserted into the AIO computer. When the earphone interface circuit detects the earphone is connected to the AIO computer, if the AIO computer is implemented as the PC, the main controller sends a first muting signal. If the AIO computer is implemented as the display, the main controller sends a second muting signal, and the signal control circuit controls and mutes the speaker according to the first muting signal and the second muting signal.