  Magnetars and central compact objects (CCOs) are subgroups of neutron stars
that show a number of properties distinguished from canonical radio pulsars. We
performed radio observations of three magnetars SGR 0418+5729, 1E 2259+586, 4U
0142+61, and a CCO PSR J1852+0040 with the Fivehundred-meter Aperture Spherical
radio Telescope (FAST) at 1.25 GHz, aiming to search for radio pulsations in
their quiescent states. During two observation epochs, no radio pulses have
been detected towards any target above a significance of signal-to-noise ratio
(S/N) = 7 from either the direct folding or blind search. We provided the most
stringent upper limit of radio flux (<~ 2 -- 4 $\mu$Jy) for the magnetars and
the CCO. For the magnetars with long periods, the real upper limits are likely
an order of magnitude larger due to the red noise. The deep radio observations
suggest that these magnetars and the CCO are indeed radio-quiet sources or
unfavorably beamed.
