Whether believing in Zoroastrianism (or any other religion) is considered a sin or not depends on the religious beliefs and teachings of the specific faith you are following.
Zoroastrianism is one of the world's oldest religions, founded by the prophet Zoroaster (or Zarathustra) in ancient Persia. Zoroastrians believe in a dualistic cosmology, where there is a constant struggle between good and evil, represented by the principles of Ahura Mazda (the supreme deity of wisdom and goodness) and Angra Mainyu (the destructive spirit).
In Zoroastrianism, adherents are expected to follow the teachings and principles of their faith, and belief in the one true God, Ahura Mazda. The religion emphasizes righteous living, honesty, good deeds, and the battle against evil. As with any religion, the concept of sin and its definition can vary based on interpretations of sacred texts and the specific sect or community within the religion.
For a more accurate understanding of Zoroastrian beliefs and the concept of sin within the context of the faith, it is essential to refer to Zoroastrian scriptures, consult religious authorities, or interact with members of the Zoroastrian community who can provide detailed insights. Respect for the beliefs and practices of others is crucial in any discussion about religion.