The latest incident adds to more than 40 self-immolations in about a year and a half.
Free Tibet said that the nomad it identified as Jopa was taken away by police after he set himself on fire in Maierma town in Aba county in southwest China's Sichuan province.
Free Tibet said Jopa was believed to be severely injured and might not survive. It said authorities had deployed military and security forces in the town.
Free Tibet previously reported that Dolkar Kyi, 26, set fire to herself on Tuesday at a monastery in Tso city in northwest China's Gansu province and that Lobsang Tsultrim, a 21-year-old monk, self-immolated in Aba county on Monday.
Supporters say the self-immolators were protesting Beijing's heavy-handed rule in Tibetan regions. China has blamed the Dalai Lama for inciting the immolations. The exiled spiritual leader denies this.