That is not what is means ... so did you sign up to pay your taxes directly on the IRS web site or get a transcript ?
https://www.irs.gov/individuals/understanding-your-cp301-notice
It has nothing to do with TurboTax.
Note the first line in that IRS article:
"If you *didn't* initiate this registration when accessing one of our online services, immediately call the number on your notice to disable your account."
I have received the same CP301 what am I supposed to do with it ? Is filling an E-return considered using IRS Online Services?
Please see the attached link for more information from the IRS regarding your notice.
It is only sent out to let you know there was activity and allow you to confirm whether you initiated the activity on your account or not.