I withdrew some mutual fund investments from my RRSP account for my startup business. I did not get any tax slip for that. Should I report this amount as income?

Yes, you need to report this as income. If you withdrew anything from an RRSP, (or any Registered accounts) you should receive a tax slip. In your case a T4RSP should have been issued. If you have not received this slip, you should contact your advisor or financial institution and request it. You may also be able to access the slip online from your CRA My Account if you are signed up for one.

If your mutual funds were withdrawn from a "non-registered" account, you must still report the income as Capital Gains.