(of part of the body) producing too much of a substance, or reacting too quickly

With an overactive thyroid, metabolism speeds up. 甲状腺过度活跃，新陈代谢加快。

Over-active bladder is a frequent and urgent need to use the toilet. 膀胱过度活跃是指频繁而迫切地需要上厕所。

(of someone's mind or imagination) thinking too much about things

She had dismissed the voices as figments of her overactive imagination. 她认为那些声音不过使自己过度活跃的想象虚构出来的。

I have a terribly over-active mind and anything that's happened in the day whirls around my head endlessly. 我的大脑总是想太多，白天发生的任何事情都会在我的脑海里无休止地旋转。