Looks like it is.
There are OTC products you can put into the ears.
Also, there are spot-on products that treat fleas, ticks and mites a well, so you can even prevent them from building up. Talk to your vet.
Does your cat shake his head, do his ears appear to be bothering him?
You could try OTC ear drops as mentioned above. Hold the bottle in your hand for a few minutes to warm it, not such a shock for your cat when you put the drops in the ears, rub the base of the ears to distribute the liquid then gently wipe the gunk out. You may have to do it each day for about a week to get them clean.