Moss can be a slippery problem on walkways and paths, especially in damp climates. If you can, improve the drainage surrounding the pavers so that the surface does not remain wet. Also remove overhanging tree limbs if possible to improve air circulation and light conditions. If the infestation is not too severe sometimes the moss can be removed with a power washer or very strong jet from a garden hose, although it will return in due course. There are a couple of good products on the market that are based on salts of fatty acids, such as Moss-Aside Herbicidal Soap from Gardens Alive and Safers De-Moss Cryptocidal Soap. Use these according to the instructions. Biodegradable chlorine bleach is sometimes used also, but it may harm surrounding plants and needs a lot of care to use properly. If the conditions that cause moss growth in the first place are nor corrected, the moss will likely return and need ongoing removal.