Many Jews have fallen victim to the deception of the messianic movement (Jews for j-sus, Hebrew xtians, etc.) Are those that perpetrate this deception tantamount to the Erev Rav in the Wilderness over 3,300 years ago?
(This business of connecting your favorite villain with biblical characters doesn't really help much, by the way. There are no halachos on the books of how to relate to an erev rav-ite. A much more sophisticated question would compare a current-day population with how halachic sources such as the Talmud or Rambam practically addressed historical groups, such as Samaritans or Karaites.)
So-called "Messianic Jews" are generally Christians who incorporate some Judaic practices, and/or try to convert Jews to Christianity (albeit their brand of it) with Hebrew-ish sounding stuff; so they'll talk about "Yeshua" instead of "Jesus."
They are not Jews, plain and simple; Judaism regards them no differently than the Christians who tried to convert Jews more overtly a thousand years ago. If one of them goes through a conversion-to-Judaism ritual with the secret intent of converting Jews to Christianity, that conversion is invalid and halacha views such a person as non-Jewish.
NOTE: I have very unpleasant things to say about someone like this. That does not, however, entitle you to break the law of your country and use violence against them.
The eirev rav is a cautionary story of people who absolutely wanted to throw in their lot with the Jews, and were allowed to do so; but their motives were complicated -- selfishness played a role -- and their old habits died hard. The better analogy here is Orpah from the book of Ruth, who went through all the motions of a conversion sincerely, but when the going got tough, couldn't stick it out.