To know if it is really the Messiah or if it is the Anti-Messiah God gives us a way to test them. You can find this test in Deuteronomy 13. Here is the first 4 verses:

“If there arises among you a prophet or a dreamer of dreams, and he gives you a sign or a wonder, 2 and the sign or the wonder comes to pass, of which he spoke to you, saying, ‘Let us go after other gods’—which you have not known—‘and let us serve them,’ 3 you shall not listen to the words of that prophet or that dreamer of dreams, for the Lord your God is testing you to know whether you love the Lord your God with all your heart and with all your soul. 4 You shall walk after the Lord your God and fear Him, and keep His commandments and obey His voice; you shall serve Him and hold fast to Him."

I would encourage everyone to read the whole chapter! Also if you are interested 119 Ministries also did a video around this chapter.
http://www.119ministries.com/teachings/video-teachings/detail/the-deuteronomy-13-test/