Mounted combat rules are complicated and don't actually work very well unless you attempt to discern rules as intended (which not everyone will agree on).
But, to be succinct and to answer this specific question: Yes, when mounted and your mount charges, you also are charging.
Mounted Combat: When making a charge while mounted, which creature charges? The rider or the mount?
Both charge in unison, suffer the same penalty to AC, the gaining the same bonus to the attack rolls and following all other rules for the charge. The mounted combat rules are a little unclear on this. Replace the third paragraph under the "Combat while Mounted" section on page 202 with the following text. Note that a "mounted charge" is synonymous with a "charge while mounted," and that when a lance is "when used from the back of a charging mount" it is during a mounted charge not when only the mount charges.
A mounted charge is a charge made by you and your mount. During a mounted charge, you deal double damage with your first melee attack made with a lance or with any weapon if you have Spirited Charge (or a similar effect), or you deal triple damage with a lance and Spirited Charge.
This change will be reflected in future printings of the Pathfinder RPG Core Rulebook