Ah, I saw this information in the forum.
Activity just increase, It can't decrease?
Yeah, activity points not only increased because your activity points will decrease by 14 points every 116 years.
Read here:
https://bitcointalk.org/index.php?topic=582736.msg6371103#msg6371103TLDR; Every 116 years you will lose out on 14 activity. Sad right ?