Will I still need to wear a mask after I get vaccinated?

At least for now, yes.

Like other coronaviruses, the one that causes Covid-19 is primarily a respiratory virus, which affects the organs and tissues involved in breathing (like the lungs). It typically enters the body through the nose and multiplies rapidly, allowing it to spread easily through exhaling, speaking, laughing, singing and sneezing. The vaccine helps the body to attack the virus, preventing a person from becoming seriously ill.

But researchers have not yet determined whether the vaccine reduces individual spread of the disease. In other words, we know that if you get the vaccine, you are highly unlikely to become seriously ill from Covid-19. But you may remain contagious to others within your social circle and to anyone you come into contact with. Until we know for sure that there is minimal risk of infecting others once you've been vaccinated, or until we reach a level that allows for herd immunity protection, you should wear your mask and practice social distancing as before.

Related Questions
What do I do if I have Covid-19 now?
Adhere To CDC Guidelines If you test positive for Covid-19, the following steps -- outlined by the Centers for Disease Control and Prevention (CDC) -- will help you care for yourself and protect others: Alert close contacts. Tell anyone you have recently come into contact with that you have Covid-19, so they can take the necessary precautions and prevent further spread. If you have concerns about confidentiality, especially in the workplace, check with your employer. Many can notify others…
Where should I go for trusted and up-to-date information on Covid-19 vaccines?
The Centers for Disease Control and Prevention (CDC) has great information on the Covid-19 vaccines, including a FAQ page. Another CDC resource will direct you to state Department of Health websites. Those sites will help you determine when you can get the vaccine in your area.
I'm young and healthy. Should I get vaccinated?
While not considered to be at high risk for severe complications from Covid-19, serious cases do occur among younger, healthier people. The Centers for Disease Control and Prevention (CDC) also warns of the potential long-term health effects of Covid-19 infection, even for those who experienced mild illness.