Yes, there are several, some easier than others. I find by far the simplest method is to use ftp. You must have a WiFi network with both the nexus seven and your Ubuntu PC logged on. Download a free package from the Play Store to your nexus 7 called ftpserver. Then download gftp from the Ubuntu software centre to your Ubuntu PC.
On the nexus seven, start ftpserver. You will see a simple screen with a start button. Turn it on. You will then see the screen update with the network address, something like 192.168.0.10, and the port number, something like 2221. The usernsme and password will also be displayed. Start FTP on the Ubuntu machine and enter those parameters. You will now be connected and be able to transfer files backward and forward between the two machines using the browser panes built in to gftp. Let me know if you need screenshots to make it clearer.