I'll say a few things about this. First, the obvious: it's important to keep in mind that the GRE is a relatively minor component of the grad school application process. Letters of rec, transcripts, research history, essays etc. all receive more attention from admissions committees. If your application is superb in all areas aside from the GRE (where your score is also pretty solid), you should feel pretty good about your chances.
But to answer your question more directly, it sort of depends on what Northwestern means when it specifies a "minimum score." It could be either of two things: it could be that the pool of admitted students historically has not frequently scored below that minimum, but it also could be that that is the point at which the admissions committee at Northwestern forms doubts about an applicant's ability to engage in PhD-level work. Obviously the latter would imply the former, but if it's only the former that is true, then I think your chances aren't particularly negatively affected by having scored near the bubble. Even the latter's being true isn't a death knell if other parts of your application are truly exceptional.
With all of that said, if it is the case that you could succeed in a PhD program (in any discipline) at Northwestern, then it's also likely the case that you can score quite a bit higher than 148 on GRE-Quant if you had time and other resources at your disposal to prepare. If you find yourself in a position where re-taking the GRE is feasible and you think you can score around 155 or so, I would give that some consideration.
Best of luck to you! Just know that, even if Northwestern doesn't accept you, you will surely get into another great program and thrive