If it's an ornamental fig like ficus benjamina or such, you will need to bring it in as Carrie said. They don't like rapid swings in temperature, either, so you may get some leaf drop when you do.
If it's an edible fig, most are cold tolerant down to 20 degrees or so, and some much lower than that. I get away with just moving them up close to the house in zone 7. In zone six I'd be more worried about the pot freezing, though, which would be hard to prevent with moving the plant to a warmer spot. Plants in pots lose a zone or two of cold tolerance. It's the trade-off for the portability that allows you to put them in a greenhouse, garage, or other sheltered spot when needed.