The ousted leader appeared to be in "good health" and asked to see her legal team, her lawyers say.
Two new charges were announced against Ms Suu Kyi, who was arrested after the 1 February coup.
Meanwhile, protesters took to the streets again despite Sunday seeing the deadliest day yet with 18 killed.
The deaths came as the military and police ramped up their response to demonstrations across the South East Asian nation over the weekend, firing into the crowds.
But protesters defied the crackdown on Monday, demanding the elected government be restored and Ms Suu Kyi and other leaders of her party, the National League for Democracy (NLD), be released from detention.
The military says it seized power because of alleged fraud in November's general elections, which saw the NLD win by a landslide.
It has provided no proof of these allegations - instead, it has replaced the Election Commission and promised fresh polls in a year.
Where has Ms Suu Kyi been?
Ms Suu Kyi, 75, was arrested when the coup began and had not been seen in public until Monday's hearing, when she appeared via video link at the court in the capital, Nay Pyi Taw.
It is unclear where she has been held over the past month, but some reports suggest she was detained at her home in Nay Pyi Taw before being moved to an undisclosed location.
Ms Suu Kyi originally faced two charges of illegally importing walkie talkies and violating Myanmar's natural disaster law, but a further two charges were added on Monday. She was accused of using illegal communication equipment and causing "fear and alarm".
The initial charges carried sentences of up to three years in jail. It is not clear what punishment the new charges might carry, but she could reportedly be barred from running in future elections if convicted.
The case has been adjourned until 15 March.