I have come across the problem before and you'll be pleased to know it is a very simple and cheap fix!
The brake fluid will need topping (maybe just very slightly) as the chassis control system senses the level is too low.
First time I experienced this I was surprised at how simple yet also how complex the system is to take the fluid level reading this precisely.
Top up the fluid to the 'maximum' level but no higher and see if the light extinguishes and does not return.
Also, consider that the fluid level may have dropped for a reason!
This could be a major problem with a hydraulic component if the level has dropped a significant amount but if only dropped slightly then it is more than likely the brake pads may have worn low.
Either way, have the brake components inspected for safety and condition