If you have the MacSoft version of Civ3 Vanilla (the original, with no expansion packs), yes. AlanH can direct you to where to find that editor. It should work even if you have the expansion packs, if all you want is a map without the extras that the expansion packs provide (which is quite a bit).
Otherwise, no. But I am working on a Civ3 Scenario editor that will work on all common platforms (Windows, Mac, Linux, etc.). The map part will be the last part I will due as it's pretty complicated. Right now I have completed all the sections pertaining to the scenario rules, such that it is equal to the Conquests (Windows) editor's capabilities, minus the map, but I have not added safeguards to keep the user from creating scenarios that are completely illegal by Civ3's definition (ex. giving a unit a negative attack value). Those safeguards are the next priority, and sometime after that, the map support.