Mycoplasma bovis has been found on a farm in Selwyn, just months after the country reached no known cases of the cattle disease.
A standard bulk tank-milk background screening picked up the infection.
The Ministry for Primary Industries (MPI) will work with the farmer to clear the farm of cattle.
MPI is tracing animal movements to identify the likely source of the infection.
"The find is unsurprising as we expected to identify more infected properties during spring testing, and it does not undermine our progress toward eradication," MPI said in an update.
"As with previous confirmed properties, we will likely see the number of farms under movement restrictions increase over the next few weeks as the programme looks for any possible infection."
MPI said although there continued to be less infection each year, this case was an important reminder for farmers to follow good biosecurity practices and record all on-farm movements through NAIT.
Back in August, New Zealand reached no known cases, after the last property was cleared of cattle and declared disease-free.
RNZ
