During the 90's I saw parts of a science-fiction cartoon on TV. I don't remember for sure, but the graphics resembled Heavy Metal, and I think it was American, but again, I'm not sure.
What I do remember is that the main character had a robot arm that looked just like a regular one. I think the humans were at war with robots controlled by an evil overlord, and someone believed the main character was also a robot because of his arm.
Another relevant memory was related to the bad guy (or one of the bad guys): in the end, it turns out it was a bratty teen who thought it was a game or who didn't realize exactly what he did.
 Based on the feedback received so far, I need to add that:
- this was a cartoon, not anime / japanese animation.
- It was a movie, not a cartoon series.
- The robots were more like androids / humanoid robots, not mecha.
I also remembered a female protagonist. She's the one who notices the main character had a robotic arm after he has some sort of accident and robotic parts become visible beneath his arm skin.
Do these details sound familiar to anyone?