That is your local IP address, Comcast has a public IP address that they've assigned to you, I sure hope you have a router sitting between you and the Xfinity router. If so, you can go into that router settings and tell is to forward all incoming messages on a particular port used by MineCraft to your local IP address..
If you don't have a router between the Xfinity router and your computer, then you can't port forward..