An asteroid in earths orbit?

It's not scary. It is what is known as a Trojan asteroid. That means it is gravitationally bound to orbit a more or less fixed distance ahead of the Earth. It isn't going to come any nearer or get any farther away. It's held where it is by the same force that keeps Earth orbiting round the Sun and the Moon orbiting round Earth. It is no more scary than the Moon, which is much larger and much closer.