The main antagonist is the main character that is the cause of conflict and, basically, the main antagonist, for lack of a better term. The central antagonist is the antagonist that the story focuses on the most but isn't necessarily the main one. For example, in Sonic Adventure Dr. Eggman is the central antagonist because he drives the story and has the spotlight most of the story while Chaos is the main antagonist because he's the ultimate source of all the conflict of the story.

Like in Monsters Inc. Randall Boggs has the most screen time and is the primary antagonist Mike and Sulley battle and attempts to kidnap Boo repeatedly. He drives the plot for the most part. But the entire thing was Henry Waternoose’s plan and he’s the final antagonist Mike and Sulley face.

Another example - Count Bleck is the central antagonist of SPM, because story focused on him, while Dimentio is the main antagonist, because he planned most of events in the game and he's final boss.