Appears to be from Kaiser Marketing - so if you have a relationship (are a customer) with them, you may or may not want to answer. Does not seem to be a number they use for important communications (like your medical records, recent tests, or upcoming appointments).
Yes, it's a marketing call. We have a household member turning 65 this year and they've already (wasted a ton of money) sent us a big glossy bunch of garbage in the mail. Resist!