Unable to load theme by specified key: ‘Magento/mytheme’ in Magento2

1. When we execute the Static deploy command on putty , we may get below issue
Unable to load theme by specified key: ‘Magento/mytheme’.
Step: 1
1. Clear cache & flush cache
2. Exectute again static deploy
Step: 2

Still if your getting issue then follow below steps  
3. Delete your theme from Database
4. Exectute again static deploy content
5. Clear cache & flush cache
6. It will work. Mean while your theme also be create from Database.