Like all electromagnetic radiation in existence, it is the result of some sort of EM radiation generation process, and in this case it is the omnipresent EM radiation as measured in the microwave portion of the EM spectrum.....remember QM has also discovered that EM radiation is omnipresent in decreasing wavelengths to the infinitesimally small of the vacuum zpe, so it is not unique.
Since this a Science and Religion forum....here are a list of concepts that are all described as being omnipresent...
CMB/R Astronomy, GR
Vacuum ZPE Science, QM
Spirit Religion
Higg's Field Particle Physics
Aether Science, Metaphysics
Dark Energy Astronomy, Science
Seems to me that the different disciplines are all describing the omnipresence through the filter of their respective specialization, and the result is like the story of the blind men describing the elephant...I presume you are familiar with it..