I guess you could always update the firmware. Other than that, It's difficult to give any more suggestions. As far as I understand, you only see these log entries when using wireless, so unless your router is doing something odd in wireless mode, my best guess, they're coming from some neighbours network. With that in mind, unless someone else has any ideas, use a wired connection or block the connections without logging.
The firmware for my router is already the most up to date.
Actually, you could allow the connection once and as soon as it happens run arp -a from a command prompt. If it sees the connection, it will give you the MAC address...
The output (right after clicking on Allow) is the same as the one that I provided earlier in this thread. Ie:
Interface: 192.168.1.3 --- 0xa
Internet Address Physical Address Type
192.168.1.1 00-24-01-56-82-b0 dynamic
192.168.1.255 ff-ff-ff-ff-ff-ff static
184.108.40.206 01-00-5e-00-00-16 static
220.127.116.11 01-00-5e-00-00-fc static
18.104.22.168 01-00-5e-7f-ff-fa static
255.255.255.255 ff-ff-ff-ff-ff-ff static
Thanks very much for your assistance and patience.