Inspect the exterior of the microwave to see if you can determine the entry point for the ants. If you think you have found it, spray a 50-50 mixture of vinegar and water around the entry point to stop ants from continuing in.
Wipe down the inside and outside of your microwave with a clean cloth and soap. Spills in the microwave may be attracting the ants.
Place a bowl or cup in the microwave with a 50-50 mixture of water and peppermint oil. Peppermint oil is known as a natural treatment for ants because it repels them. Power on your microwave to heat the mixture until it boils.
Come back to the microwave after a couple of hours to see if you have any additional ants. You may have to repeat the extermination process more than once to completely get rid of the ants.