Ono says she was trying to be "practical" in asking that Mark David Chapman remain behind bars for fatally shooting the pop legend on Dec. 8, 1980, outside Lennon's Manhattan apartment building.
Chapman, who has been repeatedly denied parole, is up for review again this month.
Lennon's widow says Chapman might be a danger to her, other family members and perhaps even Chapman himself.
Ono made her remarks at a meeting Thursday of the Television Critics Association. She was discussing a new PBS documentary on Lennon's life in New York in the 1970s that is scheduled to air this winter.
The former Beatle would have been 70 in October.