[841] This page could not be found

.vue

        <ul>
            <li><nuxt-link to="/index">Index</nuxt-link></li>
            <li ><nuxt-link to="/about">About</nuxt-link></li>
            <li><nuxt-link to="/mobi/user/mine"> Mine</nuxt-link></li>
        </ul>

running on 'http://localhost:3000' and access to 'http://localhost:3000/about'

I click the Index and want to access the page of 'index.vue',but the error message on the page,and the url is http://127.0.0.1:3000/index

 404, This page could not be found. Back to the home page

So,how can I access to the default page?