Portscan Intrusion

Hi, Norton Internet Security 2009 frequently blocks a Portscan intrusion from the IP Address of my other computer, I don't know what it is, it usually comes up about an hour after I turn off the other computer. I don't know if that computer has a virus because each time I scan nothing is found. Can someone please help me with this, and tell me if its a virus or anything bad? Here's the info:

 

Risk Name   Portscan

 

Severity   Medium 

 

Attacking Computer   192.168.1.1, 53

 

Destination Address    MAXMINI (192.168.1.2, 63438)

 

Source Address   192.168.1.1

 

Traffic Description   UDP, Port 53

 

Please reply and tell me if it is a virus or anything bad!! I need help!!