Not by post count, nor frequency. It needs to be a bit of a pattern.
PC is more than it's forums, and I'm oftentimes active not on here, but on Discord. I'm very much in heart, a living beating part of the community. I may not seem to do much, but that's because my action is with friends, behind the doors of private interaction, but still very much involved with and involving PC.
So yeah, what matters is in the heart. Are you active here? If your heart says yes, then you are.
I am active. Maybe not in the conventional "Notice Me Senpai!" Sense, but definitely in the "Supportive friend and member" respect. I spend more time supporting others than I do trying to shine for myself.