Maybe or maybe not, do you know exactly what the buzzing is/coming from?
If it coming from the master cylinder, then it's most likely the ABS booster pump electric motor running, it should only run for 10 or so seconds when you first start your T4R and then again about every 3 to 4 times you press the brake pedal, if it's very noisy the motor may need replacing or if it runs with just a light buzzing sound and runs more than the 10 or so seconds then it sounds like the motor is good and either the accumulator is not hold pressure and or the pump itself is going bad and can't build up pressure, my guess would be the accumulator, they have been known to either have it's O-ring go bad or the accumulator itself.
If the motor is running all the time, noisy or not there's another issue with holding or building pressure..but if it very noisy you can get a refurbished motor last I check for around $300 or so but maybe more now, the only way to get a new motor is buying the pump and motor together, a new accumulator will run you $276.43 and $3.32 from McGeorge Toyota, you can get the pump and motor together for $695.27 but you would still need the accumulator, the entire pump/motor/accumulator together goes for $1052.79, or you can get the complete master cylinder assembly for $1931.14 but it might take going to the dealership to get it installed properly, mainly the bleeding of the ABS system/module.
The electric motor and or the accumulator can be installed without removing the master cylinder but would be easier to remove the master cylinder but then you would have to bleed the system, the pump I'm not sure if you need to remove the master cylinder or not to install it.
Link to the parts, prices I listed above.
Hydraulic System for 2008 Toyota 4Runner | Toyota Parts
Another option is taking a chance and getting a used complete assembly off eBay but you need to make sure you get the exact one you have now as the assemblies are different for some 4th gens years and of course you don't know how much life it has left.