Yes, it is normal and a good sign if the bag your scoby is in appears to be filled with air. This is likely due to the production of carbon dioxide (CO2) during the fermentation process. The CO2 is produced as a byproduct of the yeast and bacteria breaking down the sugar in the sweetened tea, and it has nowhere to go but into the bag. The presence of CO2 in the bag is a sign that the kombucha is active and healthy. If you have any concerns about the condition of your scoby or the fermentation process, you can contact us at support@thekombuchacompany.com for further assistance.