No, there is no Offline mode, but there are 3rd party applications created to support that. Firstly, you will need a browser plug-in to download the necessary files and then a player to open that file, even if you don't have Internet access.
Download the UniPlayer developed to play the necessary files: http://www.nibiirosoft.com/Product/UniPlayer_en.html
Download the Browser plug-in: http://www.chromeextensions.org/music-videos-photos/getflash/#.VczLMflVhvF
The browser-plug-in will display a Download button above the Unity project. Right click it and choose Save as. The file offered will have .unity3d as extension.
Open the UniPlayer and go to File > Open. Load the file and that's it.
Note: Chrome browser needs to be installed to install the plug-in.