Currently, I didn’t find a user interface method to display all ongoing deployments.
However, as always PowerShell is our friend!

The Get-AzureRmResourceGroupDeployment cmdlet gives you all deployments, whether they are ongoing, failed, or succeeded.

As an input of this cmdlet, you can target the resource groups you desire with the Get-AzureRmResourceGroup cmdlet.

For example, if you want to see all deployments of all your resource groups

Get-AzureRmResourceGroup|ForEach-Object -Process {Get-AzureRmResourceGroupDeployment -ResourceGroupName $_.ResourceGroupName}|Select-Object -Property DeploymentName,ProvisioningState

And if you want to see only ongoing deployments, just use the Where-Object cmdlet to filter the result

Get-AzureRmResourceGroup|ForEach-Object -Process {Get-AzureRmResourceGroupDeployment -ResourceGroupName $_.ResourceGroupName | Where-Object ProvisioningState -EQ 'Running'}|Select-Object -Property DeploymentName,ProvisioningState