Activity Monitor : #tmpDBCCinputbuffer

In Activity Monitor you see a mystery command, apparently executed by yourself, with 2 open transactions and coming from application 'Microsoft SQL Server Management Studio'.

Double clicking the row, gives you the Last Transact-SQL command batch >
" create table #tmpDBCCinputbuffer ([Event Type] nvarchar(512), [Parameters] int, [Event Info] nvarchar(512))
insert into #tmpDBCCinputbuffer exec ('DBCC INPUTBUFFER(319)')
select [Event Info] from #tmpDBCCinputbuffer "

Simple Answer is DONT PANIC!

It is simply the tsql generated by viewing process info in Activity Monitor itself.
The DBCC command you see is it fetching the information from the last time you double clicked an Activity Monitor row to see the last TSQL.

Of course, the irony of this is that by looking at the row, you've now changed the data.
You're looking at a system process row generated by looking at the system processes...