Nope Cable Plant tap. Most infrastructure you should see the utility company's name on it. In my neighborhood we have the same green pedestals every other house or every 3 houses and this is for underground coax drops.
Re: Is this a FIOS junction box? what it is used for?
Yea that's defiently for cable not fios. Brighthouse uses them around where I am. Fios are usually flat with the ground and say Verizon in big letters on them.