What are you trying to ask here?
Weapons have static stats, they don't 'go up' because they are manufactured things...
OP, are you worried that the monsters get harder but your weapons don't get better?
If so, then there are two answers:
1. Your weapons are expected to get better because the general course of play should have you finding magical weapons. As you progress, you either find better and better magic weapons, or you have your existing weapon enchanted to become more magical.
2. Your weapon may or may not get better, but every time you level up (depending on class; for some of the less fighter-like classes it's not quite every time you level up) YOU become better at using your weapons. You get more Base Attack Bonus, you learn feats to hit better or do more damage or do other stuff like Disarm or Trip or Power Attack (hundreds of options here).
Put that all together, YOU get better and you find better weapons.
In short, you'll be fine.
And if you are looking from the GM side with giving the monsters weapons.... well.... just give them weapons..... equipment is one of the most easily slotted out parts of a creature when you are designing encounters.
I might, might, consider raising effective CR by...maybe 1... if you really give them an upgrade though (ie- goblin with a club and leather armor going to full place with a falchion). Similar concerns if you give them the various magic items (weapon, shield, or armor with enhancement bonuses; various protective items like cloaks of resistence or amulets of natural armor). But it usually isn't that big of a buff, so it isn't that much of a concern unless you take a monster with sucky equipment and then totally bling it out.