Network Security Map - Unknown Device

I’m quite tech savvy myself, but I haven’t been able to defeat this problem, if it even is one. I’m on the “Network Security Map” on Norton 360. I noticed a device that has shown up with an IP/MAC address I can’t seem to figure out what it goes to. My computer and cell phone are connected to my network and I have those mapped, but there is a third device. My Wi-Fi is protected and I have yet to hook my Game consoles up to the network. Nothing has touched this network EXCEPT these two devices (by my doing). What could this be? Is my Router tricking itself and listing itself or…? I’ve set the trust level to RESTRICTED while awaiting knowledgeable responses.