In captivity female chameleons will produce eggs even if they haven't been mated, however these eggs won't be fertilized and therefore won't hatch.
For as far as I know this has not been observed in the wild and I would be surprised if it does happen in the wild since it is a huge waste of energy and a huge risk for the female.
I think it happens in captivity because the animals are always well fed and even overfed, so maybe their reproductive system goes in overdrive. (very quick and dirty explanation of what I think is happening, but I hope it get's the point across)