It is difficult to help you without further info because you can do this with several AI settings.
What did you use, exactly ? And did you create the package or used one alreay in game ?
Normally, just checking the weapon drawn box with a guard, patrol or travel package is enough for the character to stand still wih weapon drawn.
Of course the NPC need to have a functional weapon (not broken) in it's inventory and at least one ammo for this weapon, or it will not use it