When someone asks "Do you believe in astrology?" you could be a smart ass and rhetorically say “Do you believe in Geography?” or “Do you believe in Japanese?”
Astrology is not a religion.
So, technically, you could always say "No."
What Would Marilyn Say?
Years ago I read a column by the late Celestine Sibley, a reporter for the Atlanta Journal — Constitution, in which she talks about having met Marilyn Monroe, early in both of their careers.
Celestine was present when another reporter was interviewing Marilyn, and Marilyn made a simple comment that referenced someone’s Sun Sign.
Celestine recounts that, when the interviewer asked Marilyn if she believed in Astrology, Marilyn responded somewhat incredulously:
“I believe in everything a little bit.”
Astrology is a Language
I personally think of Astrology as a language — a jargon such as you’ll find in any industry or field of study — a vocabulary for describing the arcane details of human personality.
You have to remember that the modern vocabulary for describing psychological profiles was only introduced in the last century. Prior to the work published by Freud and Jung, Astrology had already been around for all of human history — it was and still remains a useful and specific vocabulary for describing the complex, somewhat intangible, subtle components of human personality, behavior patterns, and the alchemy of relationships.
I could easily argue that Astrology is the first-born daughter of Wisdom and Mystery and the grandmother of all Science itself.