I think it can be a sign of both. I think it's natural to have some jealousy, even when you're in a stable relationship. Sometimes people get worried about their partners friends.
I think it comes down to communication. Because often jealousy comes from not knowing, or being worried about what could be happening. It's like a paranoia. And I think if it goes unchecked, it can cause a problem in your relationships. Talk to your significant other about your feelings, if you're jealous, let them know. It becomes a problem when you're constantly jealous and question your partner. At that point, the relationship is likely over or seen its best days.
