The government had been easing restrictions imposed two months ago to try to prevent the spread of Covid-19.
Shops, restaurants and hair salons had been allowed to re-open. But they now have to close again.
The efforts to fight the coronavirus have had a crushing impact on the economy, which was already in a dire state before the pandemic.
Lebanon started negotiations with the International Monetary Fund (IMF) on Wednesday to secure financial assistance it urgently needs.
Lebanon has reported 870 confirmed cases of Covid-19 and 26 associated deaths.