It is well-known that the asteroids in the main belt trapped in the 3:1 Mean Motion Resonance (MMR) with Jupiter (at semi-major axes ～2.5 AU) are few in number, forming one of the so-called Kirkwood Gaps. Wisdom pointed out that chaotic motion of such asteroids can increase their eccentricities and make them approach and cross the orbit of Mars (or even the Earth). We numerically investigated the orbital evolution of the asteroids involved in 3:1 MMR (NEOs) over millions of years and revisited the dynamical mechanisms of trasporitng such asteroids into the NEO region. The results show that the dynamical evolution of the asteroids around 2.5 AU is mainly dominated by the 3:1 resonance, the υ5 and υ6 secular resonances and the Kozai resonance, and these bodies can evolve into NEOs through several of the dynamical mechanisms, so indicating possible dynamical origin of the NEOs.