From your description, I understood that you're trying to evaluate the mean and standard deviation values for each of the 16 matrix values that you have inside your struct matData. So, your output results would be 16 values for mean & 16 more for standard deviation.
If that's the case,
len = numel(fieldnames(matData));
meanArr = zeros(1, len);
stdArr = zeros(1, len);
for idx = 1:len
data = matData(idx).average_final_results;
meanArr(idx) = mean(data,'all');
stdArr(idx) = std(data, 0, 'all');
Documentation links for mean & std.
Note: Since you've not mentioned what exactly you're calculating std for, I've gone ahead and assumed a simple case and calculated for the entire matrix.
Hope this helps!