Is there a credit hours requirement for applying to a masters course?
No.

Since there is no universal standard for what constitutes a "credit hour", imposing a required number of credit hours is simply impossible.  If you have a degree, you have a degree.

On the other hand, which courses you've taken definitely does matter.  For example:


If you're applying for graduate school in computer science at X, but your classes have small overlap with the undergraduate computer science program at X, that raises a red flag.  That gap makes your undergraduate program look weak, or at least that it develops a different set of skills than the grad program at X normally expects.
If you claim in your application that you're interested in (say) artificial intelligence, but you've never taken an artificial intelligence class, that raises a red flag.  How an you claim interest in a field you've never been seriously exposed to?  How can we judge your abilities in a field where we can't see a single grade?


Of course, all this is secondary to your potential for research excellence, as described in specific and credible detail in your statement and in your recommendation letters.

(I'm on the graduate admissions committee in a US CS department.)