In his Mishneh Torah, Hilchos Melachim 11:1, the Rambam writes,
In the future, the King Mashiach will arise...Anyone who does not believe in him, or does not await his coming, denies not only [the statements of] the other prophets, but also [those of] the Torah and of Moshe, our teacher.
Implied in the Rambam's statement is that even if a person believes that ultimately Mashiach will come, but does not anxiously await his arrival, he is considered to have denied Judaism's fundamental creed (Chiddushim U'Biurim BeShas, Vol. III, ch. 40).