AWS Aurora MySQL Serverless CPU utilisation is above 10 even it is not processing any requests
Run show processlist or an analogous command. 10% doesn't seem unreasonable but the database is obviously doing something at this time.

It seems as though this product puts a large emphasis on replication and durability. From the product description, "Amazon Aurora is designed to offer greater than 99.99% availability, replicating 6 copies of your data across 3 Availability Zones and backing up your data continuously to Amazon S3" https://aws.amazon.com/rds/aurora/

What I'm getting at is that 10% cpu usage could likely be the result of synchronization/replication thread(s).