How can you select text in a windows command prompt without using the mouse?
As Ignacio said however you need to ensure "QuickEdit Mode" is enabled from the CMD properties.
ALT+Space -> E -> M (now in mark mode)
move the pointer using arrow keys
Hold shift and select the area to copy
Hit Enter and it's now on the clipboard
AltSpace, Mark, arrow keys, hold Shift, arrow keys, Enter.