If your printer displays an offline message, it is due to a communication failure with your Mac. Users' questions, such as why is my printer offline Mac, can have a variety of causes, ranging from connectivity issues to printer malfunction. To make it online, go to "System Preferences" and "Print & Scan." Select the printer from the Printer list and double-click it if a yellow light blinks next to its name. Then select "Resume" from the drop-down menu.