Not necessarily. It is all in the context of your education. If the rest of your GPA is fine, and it's not full of withdrawals or incompletes / etc., then I think it is fine and in some cases admirable. You may be really interested in astrophysics, but an art history major. P/F would be a good way to take astrophysics. No one has time to scrutinize your transcript. Reviewers have, maybe, a minute, so just focus on GPA.