During the second day of martial law declared by President Pervez Musharraf, police raided the homes of opposition party leaders and activists and confiscated the equipment of journalists covering the raids, The Washington Post reported.
The crackdown was intended to prevent public demonstrations that had been planned for Monday, The New York Times reported.
Sunday was mostly quiet and there was no formal curfew, the newspaper said, but authorities broke up several small protests.
Among those arrested were school teachers, lawyers, the acting head of the political party of former Prime Minister Nawaz Sharif, and members of the political party of former Prime Minister Benazir Bhutto, the Times said. The head of Pakistan's human rights commission was reported to be under house arrest.
Human Rights Watch, an international advocacy group, condemned the reported arrests as "an appalling attack on human rights defenders."
Musharraf, in a television address Saturday -- hours after declaring emergency rule and replacing the supreme court chief justice -- said militant violence and an interfering judiciary forced him to impose the emergency rule.
Musharraf said Pakistan was "on the verge of destabilization" and he would not allow Pakistan "to commit suicide."