it's not a good idea to put anything in the microwave without water. Microwave oven only work because they are tuned to vibrate water molecules. The vibration creates the heat. If there isn't an abundance of water then just about anything can happen.

You would be better off sterilising the jars with them 3/4 full of water. It'll get superheated in the microwave, so no germs will survive. And your best pink oven mits to remove em.