It is not. In Russia and Belarus groups of people of anti-government views sometimes do what they call protest in “flashmob” style. I googled topic, and I found that in 2011 some groups announced such protest-mob actions with clapping. read more
So, as far as I see, it looks like not “clapping is illegal”, but usual “anti-government protest vs police and government” story. read more
Belarus is the only country on the continent that holds political prisoners, a term which Europeans thought they had relegated to the jungles of Latin America, the deserts of the Middle East, or the Oriental tyrannies of Asia. read more
Belarus, after all, remains in a Soviet hangover, with one of the highest ratios of security agents-to-citizens in the world and a vast public sector whose livelihoods depend on a state-controlled economy. read more