No, you should not put Neosporin or any other human medication in your cat's ear without first consulting with a veterinarian. While Neosporin contains antibiotics that are effective against some types of bacteria, it is not recommended for use in cats due to the potential for toxicity and other complications. Cats are sensitive to many human medications, and some ingredients in Neosporin, such as neomycin and polymyxin B, can be harmful or even toxic to cats if used improperly. Additionally, Neosporin is not effective against all types of ear infections that may occur in cats, and using it without proper diagnosis and guidance from a veterinarian can potentially worsen the infection or cause other complications. While a small amount of triple antibiotic ointment containing Neosporin may be safe to use on a cat's skin behind the ears in certain situations, it is important to note that it should only be used under the guidance of a veterinarian.