Effectively, no, there isn't a difference.
They are both Normal-Typed, with 5 PP, max. of 8. They have the same effect, ensuring the next attack will hit. As for why they have both, only Game Freak can give a definitive answer. But, Lock-On seems more mechanized, while Mind Reader is more Psychic. They could have all Pokemon learn one or the other, but they've already introduced them both, so there's no point now in switching the moves.