Both are correct. BTW, you don't say "cat" in Enlgish! You say: "a cat", "the cat", "cats". Likewise you don't say it in Japanese. In fact: It's a cat = Neko....or...Neko desu.

"Neko「ねこ」" means "cat." 　"Desu「です」" means "is". "Desu「です」" is honorific word．Its simplified word is da「だ」.Strictly speaking，"~wa~desu「～は～です」" means "is" For example： これはねこです。 あなたは学生ですか？

"Neko" means "cat." That's the word you'll find in your dictionary. "Desu" means "is." So "neko desu" means something like "it's a cat," "I'm a cat," etc., depending on the context.