What's the name of your main male character?
Of course it is.
What's the name of your main female character?
Now, look at your query.
Do you call him Buttonweezer and her Betty?
Calling a man by his surname, and a woman by her given name might indicate unconscious sexism in your writing. Watch out for it.
Specific need trumps general guideline in these cases of course.
Just make sure you've decided there is a reason if you do this.