Raised, white dots on leaves that do not wipe off are common cell structures on ficus leaves. They are most frequently observed on Ficus elastica but may be present on other ficus houseplants as well.

These dots are lithocysts which are large cells that protrude from an interior layer of the leaf onto its surface and contain a mineral deposit called a cystolith (cell rock).  There are a number of theories regarding their function  but it is commonly believed that they enhance photosynthesis efficiency by improving light absorption. They are natural and nothing to worry about.

Courtesy of the NYBG Plant Information Service