Could be either - best thing to do is to take your machine to your local Apple Store or an AASP and have them look at it. They'll be able to tell you if it's a problem with the MagSafe adapter or with your battery or power supply. Kind of hard to diagnose yourself, much less over the Internet.
Well it could be either, You could start by restoring the macbook, if you have an external hard drive to back up to. Also before you take it somewhere just buy another charger. They are around $20 on ebay, and it would be cheaper than having someone look at it probaly. If none of those work you can assume it is thee Macbook