The kidnappers attacked the diplomat not far from the Japanese Embassy in Sanaa, later fleeing with the man's car, a security official said.
The official did not provide the diplomat's name but said he was taken to hospital and that his injuries were not serious. The official spoke on condition of anonymity as he wasn't authorized to speak publicly to journalists.
Japanese Foreign Ministry spokesman Masaru Sato confirmed that an embassy official was attacked by an unspecified number of armed robbers as he tried to get into his car.
``We are still in the process of confirming and gathering information about the attack,'' Sato said. He declined to give further details, though he noted that Japan's Foreign Ministry has issued a safety warning to Japanese tourists and residents in the area, citing the increasing danger of attack.