You should not want to ignore this message - it is a very important one which helps you identify when your computer is connecting to something which it doesn't trust, or that has a trust level which doesn't match that expected.
For some background have a look at this question on Certificate Chains
If your browser is up to date and you are accessing a valid website (especially a bank) you should not get this sort of message. The fact that you are getting this message could mean one of two things:
- the site admins have messed up the certificate. This does happen on occasion.
- your connection to the website has been compromised. This could be due to a trojan or a man-in-the-middle attack, but you should not trust the connection.
In the first case you could contact the site admins to check whether they need to correct their certificate.
In the latter - you may need to remove malware from your machine, or in the worst case, entirely wipe and rebuild it.
Have a look at the questions tagged certificates over on security.stackexchange.com for more info.