A 41-year-old Namibian man was diagnosed with the disease on Monday and is being treated in a hospital in the capital Windhoek, Health Minister Bernard Haufiku said in a statement.
Namibia has banned South African imports of processed meat products, and Haufiku warned Namibians not to eat any items still for sale in the country.
“This is the first case of listeriosis reported in Namibia since the outbreak in neighbouring South Africa,” Haufiku said.
“Our surveillance and monitoring systems are in full force.”
The victim, whose medical condition was described as stable, bought so-called Vienna sausages in his hometown of Tsumeb, in the north of Namibia.
Since January 2017, more than 900 people in South Africa have contracted listeriosis, which is caused by bacteria which can contaminate fresh food, notably meat.
Earlier this month, the source of the outbreak was finally traced to a food factory owned by Tiger Brands, 300 kilometres (185 miles) northeast of the South African capital Pretoria.
The plant produced a range of ready-to-eat chilled meats.
The United Nations has previously said that South Africa’s listeriosis outbreak is believed to be the largest-ever worldwide.
Listeria contamination can result in a flu-like illness, infection of the bloodstream and, in severe cases, infection of the brain which can prove fatal.
Infection mainly affects children and has a three-week incubation period, making it difficult to track.
Other countries that have imposed restrictions on South African meat imports are Botswana, Kenya, Malawi, Mozambique, Swaziland, Zambia and Zimbabwe.