You can add the ip-adress to your firewall list, and tell your firewall to drop all communication from that adress (replace the 10.11.12.13 with the adress you want to block):
/sbin/ipchains -I input -s 10.11.12.13 -j DENY -l
This will be lost after a reboot, I'm not sure where you can store this.
There are some packages that can do this: Acid / Guardian. I've made my own script that applies adresses that I want to block and checks every hour if the block is still in the rules, and re-applies the rule if neccesary.