Probably depends on a lot of factors, there are obviously people here who lost weight, but technically I'm not one of them.
I'm a car-free commuter, 4.5 miles to work each way plus all other errands. I've been at it almost a year and still weigh the same. I know I have shed some fat though, and built muscle. But if you're watching the scale you might be in for some really slow progress (probably depends on how much you weigh now, your gender, and diet as well).
I started cycling because it's easier on the knees than jogging, but found it was also super practical for transportation. I wouldn't buy a car now if you paid me...so weight loss is pretty far down on the list of "reasons to bike". Just get a bicycle regardless. You'll love it.