You mean a character that you have linked to a scene object?
1. unlink the npc characters starting position in the npc characters properties tab.
2. use the set character to object or set character to position action part to bring in the character when you want it to be in the scene.
3. alternatively you could set the character opacity (visibility) or use Lua to enable / disable the character with...
Characters["character name"].CharacterActive = false -- hide character & prevent interaction
-- or...
Characters["character name"].CharacterActive = true -- show character & allow interaction