"The nature of social media has given rise to strange practices contradicting morals, customs and norms," Sheikh Saud al-Shiraim said during weekly prayers at Mecca's Grand Mosque, the official Saudi Press Agency reported.
"People are using their fingertips to think instead of their minds and tongues," he said, adding that the ease of online communication has detracted from the "grandeur and importance" of the spoken word.
"This has removed a lot of the reservations or barriers of the spoken word that would normally not be uttered in front of people," he said.
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Saudi Arabia is founded on ultra-conservative Wahhabi thought but more than half of its citizens are under 25, spending much of their time on social media platforms such as Twitter, away from official strictures and traditions of the Muslim kingdom.
The country bans alcohol, public cinemas and theatres, and men and women not from the same family are segregated in public.
But there are pressures for social change.
As part of wide-ranging social and economic reforms to diversify the country's oil-dependent economy, a new entertainment authority has begun to slowly introduce foreign shows, music and other events seen by limited audiences.
Saudi Arabia's highest-ranking cleric, Grand Mufti Abdulaziz al-Sheikh, warned in early January of the "depravity" of cinemas and music concerts, saying they corrupted morals.