example.feature

  @javascript
  Scenario: confiming when saving inactive
    Given I expect to click "OK" on a confirmation box saying "Are you sure?"
     When I press "Save"
     Then the confirmation box should have been displayed
      And I should see "TV" in the "Campaign Keywords" section

steps.rb

Given /^I expect to click "([^"]*)" on a confirmation box saying "([^"]*)"$/ do |option, message|
  retval = (option == "OK") ? "true" : "false"

  page.evaluate_script("window.confirm = function (msg) {
    $.cookie('confirm_message', msg)
    return #{retval}
  }")

  @expected_message = message
end

Then /^the confirmation box should have been displayed$/ do
  page.evaluate_script("$.cookie('confirm_message')").should_not be_nil
  page.evaluate_script("$.cookie('confirm_message')").should eq(@expected_message)
  page.evaluate_script("$.cookie('confirm_message', null)")
end

you have (retval = "Ok") rather than (retval == "Ok") which is likely the problem

Thanks a lot.Will try this out and let you know.