I'm using the term 'pre-Christian' pretty broadly and wondering if I should split this question into several separate questions such as:
Was there anti-Semitism among eastern European pagans who were conquered by the Teutonic Order and associated Christian crusaders?
in Scandinavia before it converted to Christianity? I'm thinking about the 'vikings' who worshiped Odin and the rest of the Norse pantheon. What about Norsemen who sailed and settled outside of Scandinavia like Normans, Rus, Varangians, etc?
among the barbarian tribes who invaded/settled in the Roman Empire during the Migration Period? Although I heard somewhere that some of those tribes were Christian so I'm not sure if this counts...
Did the Romans persecute Jews? For example I know that various Emperors persecuted Christians, so did they ever do the same to Jews? Also, should the suppression of the various Judean insurrections be characterized as political or ethnic violence? If the latter, did the sentiment extend beyond the regions/events of the insurrections?
Briton, Celtic and Germanic 'barbarians' such as those the Romans encountered/fought in the Republic and Principate periods. Had the Jewish Diaspora even reached these regions by that point?
anywhere/when else. These are just the main scenarios that I could think of.
While there has been persecution of Jews throughout history, "antisemitism" refers specifically to an ideology that arose in the mid 19th century and has colored almost all racial hatred towards Jews since then. The word implies a belief in a malevolent Jewish conspiracy to control various circles of power and carries an ideological imperative that "they must be stopped". Propaganda hoaxes like The Protocols of the Elders of Zion spread the belief very effectively so that anyone with hatred or mistrust towards Jews as outsiders of their community picked up on the stereotypes and added them to their personal narrative of racial hatred. Despite the massive drop in antisemitism after the second World War, the 19th century conspiracy theories have remained common among white supremacist, Islamic, and conspiracy theory circles.
This question is, for the most part, unanswerable. Documentation of Jewish communities outside core Jewish areas of the time (which were mostly in the Middle East) is quite sparse. And there don't seem to have been Jews in many of the areas you mention. While it's possible a Jewish trader ventured into Scandinavia at some point, that's not something likely to be documented, and not really enough to say whether or not Scandinavians hated Jews. Same with the groups the Romans fought with, only it's much less likely they would've ever encountered Jews. And by the time various other groups migrated into Roman territories, they were Christian (at least, when they're discussed in the book I have on the subject they are). There actually may well have been Jews in prechristian Eastern Europe, but they're not terribly well documented either.
Anyway, there was lots of interaction between Jews and Romans. And it was, as you noted, not always pleasant, with a few very gruesome wars. But it wasn't just political--Jews and Greeks had a few notable riots/street fights/etc in various places in the Mediterranean. It's not entirely clear as to why, exactly, and it doesn't really count as persecution in the modern sense. Jews did live in much of the Roman empire relatively free from discrimination specifically aimed at them (as opposed to just not enjoying the privileges of not being Roman, which isn't specific to being Jewish), though their relationship with various non-Jewish groups was sometimes strained. This is hard to descibe in sub-book length, so I'd like to recommend Jews Under Roman Rule: From Pompey to Diocletian.