You could go to the manually configure option and check the details and then configure out the type of access, when you get to computers and communications options it will give you specific info about the attempt and then you can understand it some.
You do have someone trying to connect; is what the Norton it seems, is telling you. The means to stopping this, by rule or whatever is understanding it. You need to dig a little. Could just go away, could be necessary connection for an update that you have permitted. May be good to run spyware check.
Are you on wireless, are you using a router, whats your setup like, installed any new programs lately , looked at your norton logs lately??
One possible explanation for what you are seeing: You get a request from a computer/address for access to a specific port, you press automatically configure and that request is ruled as blocked and then you get a request from same address for access to a different port, repeat often. It depends on the info you see in your logs as to what this type of situation could mean. Could just be someone scanning a range for any reason.
If you manually configure your rule you can block all access from a specific address to all ports and protocols: Block all communication in/out. Norton is actually an OK firewall if you turn off "Automatic Program Control", understand rule sets, watch your logs and set it to stealth your ports.
