Depends on what you mean.
The first RPG I designed on a mental level was a Christian themed RPG with 3 attributes for your character - Faith, Hope, and Charity, and a list of virtues for skills: joy, peace, forbearance, kindness, righteousness, faithfulness, gentleness, self-control, prophecy, service, teaching, encouragement, generosity, leadership, etc. This was back in the early to mid 80's in response to the occult scare. Game play as I envisioned it would be something like the game Fiasco, only with the goal of ending the scenario in a good place. Unfortunately, there were two fundamental problems. First, I was like 11 and I'm not sure I had the skills to do the project then - though I still feel the simple mechanics I was going with were pretty sound for a game of its type. And secondly, and more importantly, the game scared me. I found its themes far too serious, the need for a storyteller to take the role of God to be outright blasphemous, the fact that as GM I'd essentially be taking the role of a spiritual life coach to be overwhelming, and it questionable whether anyone who had the maturity to play the game the way I intended wouldn't be better off living life for real rather than just pretending to. In context, I decided that maybe fantasy polytheism wasn't so bad for a game after all precisely because a game shouldn't be serious.
The first RPG I actually started to commit to paper was a fantasy heartbreaker attempting to fix the realism problems I had with D&D combat mechanics. Unfortunately, I was 17 and didn't have the skills to complete the project, the mechanics were a mess because I hadn't yet realized that realism wasn't a good goal in and of itself, and the whole thing ended up being so complex that it could only run on a computer - at one point I started coding it for a MUD combat engine. I look back on it now and realize that my 11 or 12 year old self was making a better more sophisticated game.
The first RPG I actually designed to a more or less completed state was basically a fork of D&D 3.0 based on my attempts to fix the problems I felt the game had with balance, etc. It's roughly as different from D&D 3.X as Pathfinder is, but its since 60% or more of the game is someone else's design, it's really no more than house rules for D&D rather than a separate game. It's really good in my opinion, and I love the results and think that its getting to be quite polished, but it's not an independent RPG.
The first original RPG I actually designed is a game I call SIPS - for Simple Imagination Play System. I designed this game for my kids to play. It's a reasonably nice little rules light system meant for the challenges of being a child. The original SIPS game involved fairy land. Right now we are playing a slightly more advanced version of the rules called SIPS for Hogwarts, which is basically the same game with a magic system meant to emulate Harry Potter's world replacing the usual superpower system.
