First contact between humanity and electrical phenomena cause by humans were based on electrostatic. I.e. rubbing an amber stick with a wool cloth would leave it electrostatically charged. The investigation on these phenomena ended up in Maxwell theoretical corpus.
Removing amber, wool and glass from your world would probably delay or impede the spark (both figuratively and literally) of electricity from touching the human.
Removing Amber can be achieved impeding the evolution of the tree species which produced it in the past.
Removing wool could happen either by eliminating sheep's and goats from the world, or altering the climate to make their domestication and usage for clothing unnecessary. I.e. in ancient Egypt line was the most used fiber, lacking the need of protection from cold weather.
Removing glass is a bit harder to achieve while not stopping at all the technological advancement of your humans.
Considering that high air humidity hampers the build up of electrostatic charges, you could also have a more humid world climate, making it more difficult to accidentally charge anything.
However, I think these attempts might just delay the inevitable: humans are curious, they cannot be stopped from searching, at most delayed. As long as electromagnetism is part of your world, they will investigate it.