It can be multiple things. You may have multiple IP assigned to your computer and your AV sees itself as the primary only. What I would do is install “active ports” at http://download.cnet.com/Active-Ports/3000-2651_4-29653.html?tag=mncol. It sees all connections on your machine within a GUI interface equivalent to running netstat -A at the command line. You may want to review your “DHCP” server (probably your router) and you can see what are the active clients are. You should be able to see the computer name assigned to those other computers. From there you can decide on who are these guys. If you don’t know them, I would recommend you secure your access from the router security feature.
1) Enable WPA or higher (if using wireless and supported on your wireless card)
2) Disable SSID broadcast (if using wireless)
3) Change default password from router
4) Enable MAC filtering (if using wireless)