There are several factors which might contribute to these concerns, even though RF emission is harmless to human. Psychologically, anything unknown may be daunting. Additionally, people tend to associate RF emission with those of hazardous types of radiation such as x-rays, although it is known that both are totally different in nature.
RF emission from mobile phones and base stations is a form of non-ionizing radiation (NIR) as compared to ionizing radiation (IR) such as X-rays. Finally, there are so many incorrect or sensationalized reports made by different individuals and groups about the negative effects of RF emission that are readily accessible through internet, triggering these concerns.