If you polled people on what anti-scientific belief they thought was most widespread, I think most would reply creationism, followed by global warming skepticism and vaccine skepticism. I hesitate to include astrology because I don't know to what extent horoscope readers believe what they're reading.
I think, however, that the most widespread anti-scientific belief is not any of the above. Instead, I think it might be what I can best describe as neuroscience denialism. It consists in denying that there is, or ever can be, a neuroscience that accounts for various subjective human experiences, such as pains, pleasures, musical experiences, loves, lusts. It denies that there can be a common neurological organization shared across people, across humanity that accounts for these things, in virtue of which we can come to objective knowledge about them.
It's motivated, I think, by people's fear that they lose power over their individuality if they concede such things to science. In my experience atheists are no less likely to make such claims than theists.