My ISP is saying im approaching my threshold for my months useage (5Gb).

Does useage only apply to when you upload or download things or does it apply all the time my computer is connected t the interenet i.e. opening webpages etc???

Ive just downloaded a Bandwidth monitor and from what i can make out it all the time...........

Is that right??/ Do I have to stop surfing the internet in order to avoid additional charges before the end of the month???