The Environment Ministry is revising the timetable for six of 11 municipalities in an exclusion zone from where residents were moved after the power plant went into meltdown following the March 2011 earthquake and tsunami.
The original plan called for completing all decontamination by next March.
Nobody has been allowed to live in the zone again yet, although the government has allowed day visits to homes and businesses in some places after initial decontamination.
Now an environment ministry spokesman said: "We will have to extend the clean-up process, by one year, two years or three years, we haven't exactly decided yet."
He said there were several reasons for the delay, including a lack of space for the waste from the decontamination work. Some residents have opposed dumping the waste in their neighbourhoods.