The attackers stabbed Nabil Sabaie in his arms, then fired a few shots in the air to disperse passers-by who gathered during the attack on one of the main streets of the capital on Saturday, his father Muhsin Subaie said.
"They pushed him to the ground, then pulled a knife, and stabbed him in his right and left arms and now he is in the hospital," Sabaie said.
No further details were available on who is behind the attack and no one has claimed responsibility.
Sabaie is known for strong criticism of Yemeni President Ali Abdullah Saleh and his policies.
In a recent article, he condemned the president for grooming his son to succeed him and appointing family members in key government positions.
Yemeni journalists have reported a concerted campaign of abuse and harassment by the government in recent weeks.