This is not enough information, not enough of a dream. It needs also your age and waking relations to horses.
Riding horses represents power and authority. Perhaps you are coming to a place in your life where you feel that you are gaining more authority.
Central images in dreams are nearly ALWAYS Bivalent, that is both positive and negative in their potential meanings. That's why it is not possible to go beyond "perhaps" without knowing more details of the image and preferably more about the WHOLE dream scene and what came before and/or after it (that is some more of the dimension of TIME for the dream as remembered.) The key issue here about the notion of power and authority is WHO IS IN CONTROL OF THE HORSE, you or the horse itself? If you're not sure, then your unconscious urges may be taking you where they are going--urges like Greed, Powerdrive, Fame/Popularity or Lust. If you ARE SURE you are in control of the horse, then you are able to direct your bodily/unconscious energies according to your conscious intentions. Your age (hence stage of life) and gender can add understanding to the dream (horse-riding in waking life is a favorite of adolescent girls). For dreams don't come to congratulate us for how well our lives are turning out, but to show us something from our unconscious life-stream that we need to become aware of consciously so that we can act in ways to include it in our direction-of-psychospiritual growth.
So if you want to get much more valuable dream-wisdom for your daily living, instead of just 2 interpreters offer inadequately informed opinions on a dream that's only a skeleton without any flesh or dreamer-background, then write more about your dream.