on (your/her/someone's...) mind

1.If there's something on your mind, you know you can talk to me about it.


2.I'd like to know what's on his mind, but he never tells me anything.


3.Whatever's on your mind, it's not good to keep it all inside. You really need to talk to someone
　about it.

何かを考えている・何かを悩んでいる