A computer system for processing data in a non-operational state and processing method thereof are provided. The computer system includes a data output unit, a data source, a data processing module and a state monitor unit. The data processing module accesses and processes data from the data source, and transmits the processed data to the data output unit. The state monitor unit monitors a power supply state of the computer system to generate a state switch signal, which indicates whether the computer system is in an operational state or a non-operational state. When the state switch signal indicates that the computer system is in a non-operational state, the data source and the data processing module receives operating voltages to access and process data.