There are 151 Pokemon if FireRed/LeafGreen in the Native Pokedex, though National contains Pokemon from the Hoenn and Johto regions, increasing the total to 386.
As fizzcube said the pokedex contains 151 Pokemon but if you look at the website I have entered in my comment you can see the Pokemon which are avaliable to be catched from other regions as well!!
Hope this helps!!
How to change your username
How to add a user avatar
Why was my post hidden?
Flags vs Downvotes
Official PokemonDb League
Type a Pokemon name, type, move or ability to see instant results.