English

They are both "correct"; it depends what you want to say.

As is generally the case, it depends on the context.

If you are referring to someone acting non-judgmental, without prejudice, then the phrase open mind is appropriate. However, the phrase empty mind is more about an individual being without any (obvious) thoughts at all.

Example empty mind:
"The yoga instructor while guiding us in a group meditation advised us to be a vessel for an empty mind."

Example: open mind
"The judge advised the individuals in the jury to have an open mind."