If your child is not "good" at school, he can lose interest. After all, few people want to continue on a path where they're seeing limited success. In some cases, an unidentified learning disability might be contributing to this defense mechanism. A child with dyslexia might "hate reading," while a child with dysgraphia might "hate writing." It's easier to pretend that you're not interested in school work than it is to admit that you might need a bit more help. The school district can help with testing to discover if this might be playing a role in his problems.
According to Psychology Today, the focus on high-stakes tests in the classroom has caused many children to lose interest in school. Teachers must focus primarily on English and math -- the subjects the tests measure -- at the expense of more "fun" subject areas, like art, music and science. Your son might be suffering the effects of this. He might also just have a teacher who doesn't inspire him, or be feeling lonely because he doesn't have many friends in the classroom. Talk to him to figure out why he doesn't like school.
Most likely, it isn't so much your child's lack of interest in school that bothers you, as it is his lack of passion for anything, or at least for something that seems like it will bring about employable skills in the future. If you can, guide him toward something that he can learn and grow in, even if that's something not taught in traditional school. For example, he could turn his interest in computer games into actual computer programming, or love of cartoons into writing or drawing his own characters.
In some cases, this malcontent will go away in time, as he gets a new teacher or finds something that interests him. If you're really concerned, though, you might talk to the teacher and principal about changing classrooms, look at other school alternatives in your area or consider homeschooling, where you can guide his learning to match his interests.