If you planted garlic in mid-October, you may have some garlic sprouts or leaves starting to show now. This happened to me last year, and has happened in other years where we have a warm Fall. "Turban" type garlics like Tzan or Shantung Purple are especially likely to come up early.
Although it is not ideal to have it coming up now, it won't affect the garlic you harvest next summer very much. Mine that came up early last year seemed to be pretty normal sized, or just a bit smaller than usual. I think the extra root growth that the garlic is developing helps compensate for the green leaves that will freeze and die back when the weather turns colder.
There isn't too much you can do about it. Just make sure your garlic doesn't dry out during this time. If you didn't do a big watering right after planting, do it in the next week. The moisture we had last weekend was nice, but the ground was very dry to start with and it will help to soak it down deep to keep it from drying out in the winter when it is often dry and windy.
Something else you may notice in the late winter is some garlic cloves showing on top of the soil, especially if you haven't mulched. This happens because of frost heaves. This, too is not something to worry about as the roots actually pull the garlic back into the ground!