ARP(4) spoofing?

[Modulok]

Would this be ARP(4) spoofing, or is it just me? How would I confirm it?

arp: 192.168.1.1 is on lo0 but got reply from xx:xx:xx:xx:xx:xx on em1
last message repeated 18 times
last message repeated 19 times
last message repeated 9 times
last message repeated 10 times
last message repeated 19 times
last message repeated 24 times
last message repeated 24 times
last message repeated 24 times
last message repeated 34 times
last message repeated 23 times
last message repeated 23 times
last message repeated 26 times
last message repeated 26 times
last message repeated 26 times
last message repeated 25 times
last message repeated 25 times
last message repeated 27 times
last message repeated 30 times
last message repeated 27 times
last message repeated 27 times
last message repeated 30 times
last message repeated 10 times
...

This is on a FreeBSD router, em1 is Internet-facing. 192.168.1.1 (em0)
is LAN facing and permanent entry in the arp cache. This happens
constantly and is slowly filling my log files.

Thoughts? Suggestions?
-Modulok-