You could do something like this:

3dROIstats -quiet -mask mask+orig epi+orig > roi.1D
1dplot -one -xlabel TR -ylabel 'ROI mean' roi.1D

Or even combine them on one command line:

3dROIstats -quiet -mask mask+orig epi+orig | 1dplot -one -xlabel TR -ylabel 'ROI mean' -stdin

For more plotting options, see '1dplot -help'. However, please recognize that 1dplot is not intended to be a publication quality graph tool -- it is just a quick way to make some graphs for internal consumption, and is lacking a lot of desirable features. So don't expect to push it too far -- if you want some fancier graphs, you'll have to load the output file (e.g., roi.1D) into something else and play with it there (e.g., Excel?).