Joe
Presumably this is on the link between your router and the ISP router ie.
R1 -> ISP Router -> Internet
If this is the setup it depends on if you have an access-list on R1 applied to the interface that connects to the ISP router.
If you don't then they will able ping you anyway. If you do have an acl then you need to add
access-list 101 permit icmp host host echo-reply
this will allow your ISP to ping your outside interface.
Jon
