Finally I solved it. I have to move dismiss popup step before delete so something like When I attempt to delete the keyword "kw1" from the index-keywords page and dismiss the popup
and my step definition is now
When(/^I attempt to delete the keyword "(.*?)" from the index\-keywords page and dismiss the popup$/) do |keyword|
page.driver.dismiss_js_confirms!
delete_keyword_from_keywords_index_page(keyword)
end