Try this:
folder = pwd; % Wherever the csv files are
filePattern = fullfile(folder, '*.csv');
% Get a directory listing.
fileList = dir(filePattern)
numFiles = length(fileList)
% Get a random index
randomIndex = randi(numFiles)
% Get the filename.
fullFileName = fullfile(fileList(randomIndex).folder, fileList(randomIndex).name)
