This is totally normal. The number you're seeing on that page is the amount of rep they have garnered for the period defined in the upper-right:

If you're negative, that means you've lost more rep within this period than you've gained.

It's not entirely bad, it just means that you've been downvoted or downvoted someone else, and so you lost more rep than you've gained. The easiest way to avoid this is to be active and involved in the community by asking good quality questions and providing good answers and edits.

This is totally normal. The number you're seeing on that page is the amount of rep they have garnered for the period defined in the upper-right:

If you're negative, that means you've lost more rep within this period than you've gained.

It's not entirely bad, it just means that you've been downvoted/downvoted someone else or offered a bounty, and so you lost more rep than you've gained. The easiest way to avoid this is to be active and involved in the community by asking good quality questions and providing good answers and edits.