Nouns ending in -eau are usually masculine.
Is cerveau masculine or feminine?
lecerveau
The rule behind it
93.1% of -eau nouns are masculine
In context
Le cerveau n'est qu'une machine compliquée.
The brain is just a complicated machine.
Je te l'expliquerais, mais ton cerveau exploserait.
I'd explain it to you, but your brain would explode.
L'ordinateur est souvent comparé au cerveau humain.
The computer is often compared to the human brain.