nohup scp ... &

scp as a background process
To execute any linux command in background we use nohup as follows:

$ nohup SOME_COMMAND &
But the problem with scp command is that it prompts for the password (if password authentication is used).
So to make scp execute as a background process do this:

$ nohup scp file_to_copy user@server:/path/to/copy/the/file > nohup.out 2>&1
Then press ctrl + z which will temporarily suspend the command, then enter the command:

$ bg
This will start executing the command in backgroud