CCTV said the six were wanted on suspicion of secession or colluding with foreign forces, crimes that the new law punishes with up to life in prison.
It named the six as Nathan Law, Wayne Chan Ka-kui, Honcques Laus, Samuel Chu, Simon Cheng and Ray Wong Toi-yeung.
Hong Kong police declined to comment.
Wong said he believed the move showed that the Chinese government was afraid of Hong Kong activists overseas.
“It proves that our advocacy work is effective. We can still do more. I am still optimistic,” Wong, who is in Britain, told Reuters.
Laus said in a statement that he believed the move was “political persecution” that violated freedom of speech and human rights.
Beijing imposed the contentious law on its freest city a month ago, circumventing the local legislature, a move condemned by some Western governments, rights groups and activists in the territory.
Critics of the law fear it will crush freedoms in a city that is a world financial hub, prompting some to flee overseas.
Supporters say it is needed to restore law and order to the former British colony after a year of sometimes violent anti-government protests.