The answer is yes--but with important qualifications.
The first important thing to know is that anyone carrying a loaded firearm in California needs to be careful not to violate Penal Code 25850 PC, California's "carrying a loaded firearm" law. PC 25850 makes it a crime to carry a loaded firearm on your person or in your vehicle in any public place.
Of course a convenient store, liquor store, restaurant or other small business is a "public place." But small businesses are common targets for crimes like robbery and burglary. As a result, many business owners would like to keep loaded firearms at their businesses to protect their merchandise, their employees and themselves.
California law does recognize this legitimate need. Penal Code 26035 PC provides that PC 25850 (California's carrying a loaded firearm law) does NOT prohibit people engaged in a lawful business, or their employees, from having loaded weapons at their place of business.
This should settle the issue. But California courts have also held that there is a difference between "having" a weapon and "carrying" a weapon. In other words, even though you are allowed to have a loaded gun at your business, this doesn't mean you're allowed to carry a loaded gun there.
What does this mean in practice? It is okay to keep a loaded firearm under the cash register, for example, or in another accessible place at your business. But it is NOT okay for you or an employee to keep a loaded firearm in their waistband, in a gun holster or anywhere else on their person.
The one exception to this is if you or an employee reasonably believe that you or they are in immediate danger and need a gun to protect you, themselves or your property. In that case it is always okay to hold or carry a loaded firearm.