Using mobile signal repeaters to cover in building is active solution ?

Yes,using mobile signal repeaters to improve in-building coverage is an active solution . 

here is why : 

Directly addresses the issue : weak signal strength is the problem ,and the repeater actively amplifies the existing outside signal to bring it inside . 

External component: the repeater is a separate device installed specifically to improve the signal . 

Requires power : mobile signal repeaters need a power source to function and amplify the cellular signal . 

Passive solutions for improving signal reception , on the other hand ,wouldn/t directly modify the signal itself . examples might be : 

Moving closer to a window ( assuming the signal is better there ) .

Using a cell phone case designed to improve reception ( these can have limited effectiveness ) .

So,while both approaches aim for better signal , a repeater actively modifies the signal itself ,making it an active solution .