Los cuernos están en tu mente

Los cuernos están en tu mente
 

que quiere decir," les cuernos están en tu mente"

That should probably be "los cuernos están en tu mente."
Without more context, a proper translation can't be given. There may be an idiomatic use or a play on words we don't know about.
The literal translation is "the horns are in your mind."

Without further context, I'd assume that this is part of a fight between a couple. One of them accuses the other of having an affair, and this is the denial. "Ponerle a alguien los cuernos" is to cuckold them.

I thought that only men could be cuckold. Can it also apply to women these days? :thinking:

The context would definitely help, but I agree with Pjt that it looks like a fight where someone thinks their partner is cheating on him/her.

Los cuernos están en tu mente -> Te imaginas que te pongo los cuernos (pero no) -> I'm only cheating on you in your imagination.

I couldn't think of a sufficiently elegant way to express it, but Angélica is spot on with "cheating".

I agree with Angelica and Pjt33. Context would help, but the interpretation seems rather spot on.

I agree with Angelica.

Already here in México the word Cuernos en tu mente o cabeza means the infidelity of both genders.

Sincerely yours.