Hi. You definitely can keep fish in a tank without plants, but I don't see why you would. Both you and your fish will benefit from some plants: fish will feel more secure and comfortable, in turn rewarding you with better coloration and natural behavior. Plants also help out with maintaining water quality. Some of the commonly available plants require no special care and low to medium light (such java moss or java fern to name a few), so there is no reason not to include them.
These are just a few reasons to keep plants in your fish tanks, there are many more and even though the fish will survive in no-plants setups, they won't look nearly as good.
Hope this helps.