you could leave them alone or buy ant powder that they take in and it kills the colony.

Ants in the compost heap are a sign that it's too dry. You need to water it well on one day and turn it a few days later, repeat if necessary. You should find that the ants move out without you having to kill them off with chemicals.

This is my composting "Bible"
http://www.recyclenow.com/home_composting/

Here is the bit about ants -
http://www.recyclenow.com/home_composting/get_advice/making_compost_faqs/my_compost_bin_is.html