A method of controlling display of a pop-up window, wherein the method is performed by an image forming apparatus, the method comprising: monitoring generation of a pop-up event during operations of the image forming apparatus; characterised by, when a pop-up event is generated determining a type of the generated pop-up event and a current state of each of devices (21,23,110) that are connected to the image forming apparatus from a plurality of states, wherein the plurality of states comprises a state where a device has requested the image forming apparatus to perform an image operation, a state where a print application for requesting the image operation is being executed as a foreground application, and a state where a print application for requesting the image operation is standing by as a background application, determining at least one target device (21/23/110) that is to be requested to display a pop-up window indicating the pop-up event from among devices (21,23,110) connected to the image forming apparatus based on the determined current state of each of the connected devices (21,23,110) and the determined pop-up event type; and transmitting information about the pop-up event to the determined at least one target device (21/23/110), wherein determining whether the current state of each of the connected devices (21, 23, 100) is the state where the print application for requesting the image operation is being executed as a foreground application comprises requesting information about a foreground application, receiving the information about the foreground application, and determining whether the foreground application is a print application; wherein determining whether the current state of each of the connected devices (21, 23, 100) is the state where the print application for requesting the image operation is standing by as a background application comprises requesting information about background applications, receiving information about background applications, and determining whether a queue of the background applications includes a print application; and wherein the connected devices comprise a user interface unit of the image forming apparatus and at least one external mobile device. monitoring generation of a pop-up event during operations of the image forming apparatus; characterised by, when a pop-up event is generated determining a type of the generated pop-up event and a current state of each of devices (21,23,110) that are connected to the image forming apparatus from a plurality of states, wherein the plurality of states comprises a state where a device has requested the image forming apparatus to perform an image operation, a state where a print application for requesting the image operation is being executed as a foreground application, and a state where a print application for requesting the image operation is standing by as a background application, determining at least one target device (21/23/110) that is to be requested to display a pop-up window indicating the pop-up event from among devices (21,23,110) connected to the image forming apparatus based on the determined current state of each of the connected devices (21,23,110) and the determined pop-up event type; and transmitting information about the pop-up event to the determined at least one target device (21/23/110), wherein determining whether the current state of each of the connected devices (21, 23, 100) is the state where the print application for requesting the image operation is being executed as a foreground application comprises requesting information about a foreground application, receiving the information about the foreground application, and determining whether the foreground application is a print application; wherein determining whether the current state of each of the connected devices (21, 23, 100) is the state where the print application for requesting the image operation is standing by as a background application comprises requesting information about background applications, receiving information about background applications, and determining whether a queue of the background applications includes a print application; and wherein the connected devices comprise a user interface unit of the image forming apparatus and at least one external mobile device.