Yes there is.
Select your first form field and go to the properties inspector in Dreamweaver. Click on the little lightning bolt icon next to the value field in the inspector. This will bring up the bindings panel.
From this you'll see a validated form entries group, click that to expand it and choose the name of the field you selected in the form to set the default value of the form field to be the validated entry value.
Repeat this for each field in your form. Now, when CAPTCHA validation fails your other form fields will retain any data entered before the form was submitted.
Hope this helps you.