To dream that you are playing an online game indicates that you are trying to escape from the stresses in your daily life. You want to be someone else. You want to be in control. Alternatively, dreaming about an online game may simply mean that you are spending so much time playing the game that the images have drifted into your dreams.
In particular, dreaming about MMO games symbolise mutual goals and teamwork. Sometimes you have to depend on others in order to achieve a goal or to move up in life. Alternatively, playing MMO games in your dream suggests that you are filling a social void in your waking life.