In the book The Electric Universe by David Bodanis, the author writes that "invisible waves stream out of from our brains with a wavelength of about 200 miles".
Is it true that the brain produces ULF waves?
Technically, yes. A wavelength of 200 miles corresponds to a frequency of about 90 Hertz, which is within the frequency of human brain waves (1 to 100 Hertz). Since brain waves correspond to moving charge, you presumably do emit some 90 Hertz radiation. It should be emphasized that this is an extremely small amount which is completely undetectable.
If the book you're reading uses that to justify some mystical nonsense, just toss it in the trash. The fact that human brains emit a negligible but nonzero amount of radiation is not very interesting, because everything does, constantly. If you're immersed in water, every motion you make will produce some tiny water waves. Similarly, every motion you make produces some disturbance in the electromagnetic field. And all of these disturbances are dwarfed by what comes out of your phone.
Sometimes, fake science books use the ubiquity of electromagnetic radiation to claim that "all beings are in resonance", that the phase of the moon can affect your mood, that you can be healed by buying their crystals, or similar nonsense. This is impossible because the human body is quite insensitive to electromagnetic fields. People are regularly exposed to fields billions of times stronger than the ones we're talking about here, to no effect, such as in MRI scanners.