As al-Hussein made her way to the courtroom, scores of female supporters, some of them wearing trousers, had rallied around her, some shouting: "Freedom, freedom!"
Police rounded many of them up and marched them away.
Al-Hussein had faced a sentence of 40 lashes following her arrest for public indecency, alongside 12 other women, during a raid at a restaurant in Khartoum in July.
Ten of the women accepted a punishment of 10 lashes, but al-Hussein and two other women opted to go to trial.
Al-Hussein, who was working as a press officer for the UN when she was arrested, has said her clothes were respectable and that she did not break the law.
She has also said she wants to get rid of Article 152 of the Sudanese penal code, which decrees up to 40 lashes for anyone "who commits an indecent act which violates public morality or wears indecent clothing".
She says the article "is both against the constitution and sharia [Islamic law]" and that nothing in the Quran says that women should be flogged over what they wear.
Women's groups have complained that the law gives no clear definition of indecent dress, leaving the decision of whether to arrest a woman up to individual police officers.
The UN staff union had also urged Sudan not to flog al-Hussein, calling the punishment cruel, inhuman and degrading.