A fictitious business name statement is not the same thing as a business license.
The County of Nevada does not require a business license.
There are two incorporated cities in Nevada County which do require a business license; they are Grass Valley and Nevada City.
If you are conducting business within either of the above named cities you will need to contact that city hall (Grass Valley 530-274-4300, Nevada City 530-265-2496).
There are some instances when you will need to file both a fictitious business name statement with the County and a business license with a city.