If you have Comcast, can people see my mac address.?

In general, no. Not that it matters much anyhow - the MAC address is only used at the very lowest network layers. For instance, if you're a Comcast user, you probably have a cable modem and maybe a wireless hub and a computer or three - the mac addresses of all that gear are only used so the modem and the hub and your computers can find each other. Anything the other side of that cablemodem won't be able to *do* anything useful with that mac address, because you're not on your local area network (LAN).

Once it leaves your LAN, it uses IP addresses to find machines.

(Note that it *is* possible for a machine to be infested with spyware that sends the mac address out to whoever wrote the spyware, but they can't use it for anything more than tracking "this is the same computer that reported that same mac address earlier").

dont matter what internet you have there is software out there that anyone can use if they know what there doing and find everything about your internet and your ip and computer

use a good firewall keep them out your computer