Component:

<!--TabComponent-->
<aura:component>
    <aura:attribute name="selTabId" type="String" default="tab1" />
    <div aura:id="data-entry">
        <lightning:tabset variant="default" selectedTabId="{!v.selTabId}" >
            <lightning:tab label="Mobile" aura:id="tab1" tabindex="1" id="tab1" title="Mobile">
                <p>Apple</p>
                <p>Samsung</p>
                <p>Lenovo</p>
            </lightning:tab>
            
            <lightning:tab label="Laptop" aura:id="tab2" tabindex="2" id="tab2" title="Laptop">
                <p>Apple</p>
                <p>Lenovo</p>
                <p>Dell</p>
            </lightning:tab>  
            
            <lightning:tab label="Tablet" aura:id="tab3" tabindex="3" id="tab3" title="Tablet">
                <p>Apple</p>
                <p>Lenovo</p>
                <p>Dell</p>
            </lightning:tab> 
        </lightning:tabset>
    </div>
    
    <div class="slds-clearfix">
        <div class="slds-float_left">
            <!--disabled the back button on first Tab-->    
            <lightning:button disabled="{!v.selTabId == 'tab1'}" variant="neutral" label="Back" onclick="{!c.back}" />
        </div>
        <div class="slds-float_right">
            <!--disabled the back button on last Tab--> 
            <lightning:button variant="brand" disabled="{!v.selTabId == 'tab3'}" label="Next" onclick="{!c.next}" />
        </div>
    </div>
</aura:component>

Component Controller:

({
    next : function(component, event, helper) {
        //Get the current selected tab value
        var currentTab = component.get("v.selTabId");
        
        if(currentTab == 'tab1'){
            component.set("v.selTabId" , 'tab2');   
        }else if(currentTab == 'tab2'){
            component.set("v.selTabId" , 'tab3');     
        }
    },
    
    back : function(component, event, helper) {
        //Get the current selected tab value  
        var currentTab = component.get("v.selTabId");
        
        if(currentTab == 'tab2'){
            component.set("v.selTabId" , 'tab1');     
        } else if(currentTab == 'tab3'){
            component.set("v.selTabId" , 'tab2');     
        }
    }
})

Output: