A wireless input device comprises a plurality of RFID tag units and keys. Each RFID tag unit is coupled with two conductive wires. Only when the two conductive wires are in a closed-loop status, the RFID tag unit can generate a responsive RF signal corresponding to a scanning signal generated by a host device. Each key is formed with a switching mechanism connectable to the conductive wires of at least one of the RFID tag units. When any one of the keys is pressed, the conductive wires connectable to the pressed key will be switched to the closed-loop status from an open-loop status, and when that pressed key is released, the conductive wires connectable to the released key will be switched back to said open-loop status. Therefore, the wireless input device can be operated without the need of internal electric power.