You could have the active class be dependent upon a boolean data value:
<th
class="initial "
v-on="click: myFilter"
v-class="{active: isActive}">
<span class="wkday">M</span>
</th>
new Vue({
el: '#my-container',
data: {
isActive: false
},
methods: {
myFilter: function() {
this.isActive = !this.isActive;
// some code to filter users
}
}
})