An alternative would be to use a DataTrigger instead of a binding converter:
<Border BorderBrush="{StaticResource BorderColorBrush}"
BorderThickness="1">
<Border.Style>
<Style TargetType="Border">
<Style.Triggers>
<DataTrigger Binding="{Binding IsActive,
RelativeSource={RelativeSource FindAncestor,
AncestorType=Window}}"
Value="True">
<Setter Property="Visibility" Value="Hidden"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Border.Style>
</Border>