cvs-default-ignore-marks is a variable defined in `pcvs-defs.el'.
Its value is

Non-nil if cvs mode commands should ignore any marked files.
Normally they run on the files that are marked (with `cvs-mode-mark'),
or the file under the cursor if no files are marked. If this variable
is set to a non-nil value they will by default run on the file on the
current line. See also `cvs-invert-ignore-marks'.

You can customize this variable.