Formal/Literal:
* Me viennent à l'esprit - This is the most literal translation and means "come to mind" or "are in my thoughts."
* Je pense à vous/toi - This translates to "I think of you" and is a straightforward way to say someone is on your mind.
Informal/More Expressive:
* Tu me trottes dans la tête - This means "You are running through my head" and implies someone is constantly on your mind.
* J'ai constamment votre/ta présence en tête - This translates to "I constantly have your presence in my mind" and emphasizes the lingering thought of the person.
* Je n'arrive pas à vous/toi sortir de la tête - This means "I can't get you out of my head" and suggests a strong preoccupation with the person.
Romantic/Affectionate:
* Je pense à toi sans cesse - This translates to "I think of you constantly" and expresses deep affection.
* Tu es toujours dans mes pensées - This means "You are always in my thoughts" and suggests a persistent and loving presence.
The best way to say "are on my mind" in French depends on your relationship with the person you're speaking to and the emotion you want to convey.