You ask an interesting question, and the answer is “Yes.” Even though Ms. is not an abbreviation, you do put a period after the s. For the record, the plural of Ms. is Mses.

The word itself came into being in the 1950s when a woman’s marital status was unknown or irrelevant. Since then, many woman have assumed this title under the assumption that it’s nobody’s business what their marital status is. After all, men have felt this way for years.