Does naxproxen prevent fever or it only reduce fever when someone is already having high fever? please, need some answers?

It can do both: if you are taking it on a regular basis it can masken the fever so if you measure your temp it will be fine but Naproxen won't treat the underlying reason for fever ,also it can reduce the fever if you took it after fever started

Naproxen: It does not prevent fever. It is also not the best for reducing fever. Ibuprofen is better.