depends on where u are storing your btc, if its on a pc - wallet , it will be safe as long as u reconnect ur pc,
I think you meant "safe as long as u don't reconnect ur pc". It can be safe even if he connects internet as long as he knows how to secure his computer from malware.
otherwise I Suggest u use an online wallet to store your cash and email encrypt it for extra protection! now days can even get mobile verification
Storing Bitcoins on an online wallet is worse than storing it in a local wallet.
it depends on whether the security of the site is secure enough and the procedures implemented so that they don't know your private key, either partially or fully. Example, greenaddress.it. They require at least 2 signatures and they cant steal it by using the only private key they have.
It's been connected to the internet, if I turn the internet off, is there a way my BTC can be stolen without physically taking my pc?
you must back up private key before you shutdown
you can back up on Hardisk external or Flashdisk
cause we not know after shutdown PC we can turn on it, or some one steal your PC
The backup part is kind of mandatory for everyone, regardless of the uptime. Stealing your PC is also easy if its turned on, main part is securing your private key. The only concern is that SSD have the potential to lose data if they are of the poor grade or stored at high temperature after a long time.