The east African nation is a relatively small producer but its coffee is much sought after by global roasters to blend with coffee from other sources offering beans of a lower quality.
Prices tend to fall later in the selling season once the best-quality beans have been sold.
Benchmark grade AA fetched $305-$306 per bag, from $179-$338 last week.
Grade AB coffee sold at $205-$270 per bag compared with $201-$276 per bag last week, the coffee exchange said.
The NCE said 22,731 bags were offered for sale, with 4,254 bags sold, fetching $967,857 at an average $187.80 per bag.
Last week, some 23,800 bags were offered for sale and 2,958 were bought, fetching a total of $691,384, with an average price per bag of $192.71.
Kenya's main coffee harvest usually runs from November to December, with the highest-quality beans sold first after they are dried and processed. Sales tend to peak around February and March.
Kenya's second, smaller crop tends to be harvested from May to June. Weather can change the timings for harvests and sales.