A device and method of managing power are provided. The device includes a user input unit configured to receive a user input from a user, an output unit configured to output information based on the user input, and a controller configured to, when the user input is not received, determine whether or not an out-focus status in which the user does not use the device has started, determine, when it is determined that the out-focus status has started, a period in which the out-focus status is to be maintained based on information about a probability of the out-focus status according to a context of the device, and stop, when the period in which the out-focus status is to be maintained is equal to or greater than a reference time period, an application executed in the device.