All body hair goes in three phases - the growth phase (anagen), the transitional phase (catagen) when growth pauses and the resting phase (telogen) which is also the point when you are most likely to shed hair.
The hair on your head, especially, has a very long growth phase - it will keep growing for years, and the transitional and resting phases are much shorter. However, a lot of other body hair, especially on the eyebrows, has a very short growth phase - just a couple of months - and this is then followed by a long resting phase in which some hair may also be lost. Different follicles start or stop growing at different times, so of course all your hair, on whatever part of your body, is never in the same phase at the same time (if it was, you would find yourself shedding a lot of hair at once, for instance).
You can learn more about the different stages of hair growth here.