This is normal to a degree. All sprockets are eccentric, so the chain will tighten/slacken as the high and low zones go past. It's purely a question of degree, with the best equipment running very (but not perfectly) true, and cheaper stuff being off by a mile or so.

Sometimes there's some slop where the rings mount, so you can loosen the chainring bolts until they hold firm but not tight. Then turn the crank until the chain is tightest. That's where the high spot is toward the front of the bike, so use a mallet to give it a rap backward, and hopefully slacken the chain. Repeat the process, working toward smaller corrections until you believe you have it as good as it's going to get, then tighten the bolts, reset the rear wheel position accordingly (so there's minimal slack a the tightest point).

FWIW - the problem is often the result of an excessively tight chain, which forces the chainring out of position.

Note - if this is a recurring issue, you'll want to take everything apart, clean to dry bare metal, and repeat the centering process. When finished, apply some wicking adhesive to help lock the chainring in position.