A mobile or mob is a non-player character (NPC) in a computer role-playing game (especially MUDs and MMORPGs). Mobs are usually the wandering, monstrous NPCs that the player is expected to hunt and kill in these games.

The origins of this usage "mob" are inexact, but most theories point to "mobile" NPCs or "movable objects".

Players usually combat a mob in some manner, typically receiving rewards such as experience points and items. Usually the combat is player initiated, however if the mob is aggravated or "aggro" it is configured so that it will challenge a player who enters its threat area. Combat between players and mobs is called player versus monster (PvM). This is opposed to player versus player (PvP) battles where the emphasis is on defeating an opposing player rather fighting than against the game system.