ehh.. depends.
usually the leafs won't start turning yellow until the plant has been in flowering for a good couple of weeks... but yes it is normal for Cannabis plants to do this.. especially during flowering. The further the plant gets into flowering.. the more yellow the leafs will get.. and eventually will and can die off completely.. and fall off the plant. So, if you see that happening in the future, don't panic. It's just the plants way of getting rid of the leafs that are no longer able to complete photosynthesis (absorb light).
Kinda like the human body.. in a way. For example, the plant is doing the same thing that our human bodies do.. when we get sick. Just use your imagination.
Hope that helped ya out.
peace.