Well, if the brake fluid is fine, yet there is a message saying "brake fluid" or "low brake fluid level", then there is a possibility that that the float sensor in the reservoir is faulty, the wiring leading to the sensor is faulty, or the computer is faulty.
Non-synthetic brake fluid.
There is a brake fluid sensor located in the reservoir at the master cylinder. When the brake fluid is low it will turn the light on.
open the cap on the brake mastercylinder reservoir and fill it to the top with Dot 3 brake fluid.
Possibly coming from a leaking brake cylinder. Top up fluid and take to a brake shop ASAP.
Low brake fluid possible
Thats the brake fluid reservoir.
drivers side under hood on fire wall
Check the ABS Dump Valve. If not operating, little or no fluid to rear brakes.
On my 03 Chevy Silverado I just added brake fluid and the message turned off.
What could be wrong is your brake fluid is low in the Brake fluid container, could be a knot (kink) in the pipes or it needs to be bled in.
If it is not a low fluid condition then you will need to pressure bleed it.
your brake fluid is probably low or very dirty.